Bulk eraser including at least three magnets configured for erasing recorded information

ABSTRACT

A bulk eraser for erasing recorded information on a magnetic-recording disk. The bulk eraser includes at least three magnets and a structure magnetically coupled with the at least three magnets to produce magnetic-flux density in a gap. The gap has a first portion, a second portion and a third portion, such that a first magnet and a second magnet are disposed with opposing end poles across the first portion. The at least three magnets and the structure are configured to produce a magnetic-flux density in the second portion sufficient to erase recorded information from a portion of at least one magnetic-recording disk in a disk-stack when a hard-disk drive is inserted into the second portion. In addition, the at least three magnets and the structure are configured to direct the magnetic-flux density in a substantially radial direction of the portion of the magnetic-recording disk in the second portion.

TECHNICAL FIELD

Embodiments of the present invention relate generally to the field ofmagnetic-recording, hard-disk drives and methods for manufacturingmagnetic-recording, hard-disk drives.

BACKGROUND

The magnetic-recording, hard-disk-drive (HDD) industry is extremelycompetitive. The demands of the market for ever increasing storagecapacity, storage speed, and other enhancement features compounded withthe desire for low cost creates tremendous pressure for improved HDDs.Therefore, scientists at the frontiers of magnetic-recording-technologyresearch are driven to improve methods for reducing the cost ofmanufacturing and are constantly striving to develop new manufacturingtools to effect such cost reductions.

A critical factor affecting the cost of manufacturing is time expendedin rework during the manufacturing process. Engineers and scientistsengaged in manufacturing research are highly motivated to reduce thetime expended in the rework of HDDs, because it goes directly to theprofit margin for the product, which can make the difference betweensuccess and failure in the marketplace. The challenges of newtechnologies such as perpendicular-magnetic recording add furthercomplexity to the daunting task of cost reductions. Therefore, thedevelopment of methods and tooling by scientists engaged in HDD researchthat can meet these challenges are crucial to success.

SUMMARY

Embodiments of the present invention include a bulk eraser for erasingrecorded information on a magnetic-recording disk. The bulk eraserincludes at least three magnets and a structure magnetically coupledwith the at least three magnets to produce magnetic-flux density in agap. The gap has a first portion, a second portion and a third portion,such that a first magnet and a second magnet are disposed with opposingend poles of same polarity across the first portion of the gap. The atleast three magnets and the structure are configured to produce amagnetic-flux density in the second portion of the gap sufficient toerase recorded information from a portion of at least onemagnetic-recording disk in a disk-stack of the hard-disk drive when thehard-disk drive is inserted into the second portion of the gap. Inaddition, the at least three magnets and the structure are configured todirect the magnetic-flux density in a substantially radial direction ofthe portion of the magnetic-recording disk in the hard-disk drive in thesecond portion of the gap.

DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the invention and,together with the description, serve to explain the embodiments of theinvention:

FIG. 1 is plan view of a hard-disk drive (HDD) drive that ismanufactured using the bulk eraser for erasing recorded information on amagnetic-recording disk in the HDD, in an embodiment of the presentinvention.

FIG. 2A is a perspective view of a bulk eraser for erasing recordedinformation on a magnetic-recording disk in a HDD, in an embodiment ofthe present invention.

FIG. 2B is a detailed perspective view of a gap of the bulk eraser ofFIG. 2A illustrating the configuration of the pole-tip portions at thegap, in an embodiment of the present invention.

FIG. 3A is a plot of the distribution of magnetic-flux density at thegap of the bulk eraser of FIGS. 2A and 2B showing the distribution ofmagnetic-flux density with respect to a disk-stack in the HDD, in anembodiment of the present invention.

FIG. 3B is a plot of the distribution of magnetic-flux density andcontours of constant magnitude of magnetic-flux density in the plane3B-3B of one magnetic-recording disk of the disk-stack of FIG. 3Ashowing a portion of the disk wherein the magnetic-flux density issufficient to erase recorded information, in an embodiment of thepresent invention.

FIG. 4A is a perspective view of an alternative embodiment of a bulkeraser showing three magnets and a structure magnetically coupled withthe three magnets to produce magnetic-flux density in a gap sufficientto erase recorded information from a portion of the magnetic-recordingdisk in a disk-stack of the HDD, in an embodiment of the presentinvention.

FIG. 4B is an elevation view of a left side of the bulk eraser of FIG.4A, in an embodiment of the present invention.

FIG. 4C is an elevation view of a front side of the bulk eraser of FIG.4A, in an embodiment of the present invention.

FIG. 5 is a perspective view of an alternative embodiment of a bulkeraser that includes seven magnets and a structure magnetically coupledwith the seven magnets to produce magnetic-flux density in a gapsufficient to erase recorded information from a portion of themagnetic-recording disk in a disk-stack of the HDD, in an embodiment ofthe present invention.

FIG. 6 is a perspective view of the pole piece of the bulk erasers ofFIGS. 4A-4C and 5 disposed on a third end pole of a third magnetdisposed in proximity to a second portion of the gap for concentratingthe magnetic-flux density to erase recorded information from the portionof the magnetic-recording disk in the HDD inserted into the secondportion of the gap, in an embodiment of the present invention.

FIG. 7 is a perspective view of the second magnet of the bulk eraser ofFIGS. 4A-4C and 5 disposed in proximity to a first portion of the gapand a second pole-tip portion of the second magnet disposed proximate asecond portion of the gap for concentrating the magnetic-flux density toerase recorded information from the portion of the magnetic-recordingdisk in the HDD inserted into the second portion of the gap, in anembodiment of the present invention.

FIG. 8 is a plot of the intensities of the magnetic field intensity(magnetic-flux density) as a function of radial distance from center ofa disk in the plane of each of four magnetic-recording disks in adisk-stack of a HDD inserted into the second portion of the gap of abulk eraser configured with five magnets to erase recorded informationfrom the magnetic-recording disk in a disk-stack of an HDD in the secondportion of the gap, in an embodiment of the present invention.

FIG. 9A is a flow chart illustrating a method of manufacturing of ahard-disk drive using a bulk eraser for erasing recorded information ona magnetic-recording disk, in an embodiment of the present invention.

FIG. 9B is a continuation of the flow chart of FIG. 9A illustrating amethod of manufacturing of a hard-disk drive using a bulk eraser forerasing recorded information on a magnetic-recording disk, in anembodiment of the present invention.

FIG. 10 is a flow chart illustrating further embodiments of the presentinvention for a method of manufacturing of a hard-disk drive using abulk eraser for erasing recorded information on a magnetic-recordingdisk, in an embodiment of the present invention.

FIG. 11 is a flow chart illustrating further embodiments of the presentinvention for a method of manufacturing of a hard-disk drive using abulk eraser for erasing recorded information on a magnetic-recordingdisk, in an embodiment of the present invention.

FIG. 12 is a flow chart illustrating further embodiments of the presentinvention for a method of manufacturing of a hard-disk drive using abulk eraser for erasing recorded information on a magnetic-recordingdisk, in an embodiment of the present invention.

FIG. 13 is a flow chart illustrating further embodiments of the presentinvention for a method of manufacturing of a hard-disk drive using abulk eraser for erasing recorded information on a magnetic-recordingdisk, in an embodiment of the present invention.

FIG. 14 is a flow chart illustrating further embodiments of the presentinvention for a method of manufacturing of a hard-disk drive using abulk eraser for erasing recorded information on a magnetic-recordingdisk, in an embodiment of the present invention.

FIG. 15 is a flow chart illustrating further embodiments of the presentinvention for a method of manufacturing of a hard-disk drive using abulk eraser for erasing recorded information on a magnetic-recordingdisk, in an embodiment of the present invention.

FIG. 16 is a flow chart illustrating further embodiments of the presentinvention for a method of manufacturing of a hard-disk drive using abulk eraser for erasing recorded information on a magnetic-recordingdisk, in an embodiment of the present invention.

FIG. 17 is a flow chart illustrating further embodiments of the presentinvention for a method of manufacturing of a hard-disk drive using abulk eraser for erasing recorded information on a magnetic-recordingdisk, in an embodiment of the present invention.

FIG. 18A is a flow chart illustrating a method of reworking a hard-diskdrive in manufacturing the hard-disk drive using a bulk eraser forerasing a servo pattern on a magnetic-recording disk, in an embodimentof the present invention.

FIG. 18B is a continuation of the flow chart of FIG. 20A illustrating amethod of reworking a hard-disk drive in manufacturing the hard-diskdrive using a bulk eraser for erasing a servo pattern on amagnetic-recording disk, in an embodiment of the present invention.

FIG. 19A is a flow chart illustrating a method of preserving security ofrecorded information in a hard-disk drive in a computer system using abulk eraser, in an embodiment of the present invention.

FIG. 19B is a continuation of the flow chart of FIG. 21A illustrating amethod of manufacturing of preserving security of recorded informationin a hard-disk drive in a computer system using a bulk eraser, in anembodiment of the present invention.

The drawings referred to in this description should not be understood asbeing drawn to scale except if specifically noted.

DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to the alternative embodiments ofthe present invention. While the invention will be described inconjunction with the alternative embodiments, it will be understood thatthey are not intended to limit the invention to these embodiments. Onthe contrary, the invention is intended to cover alternatives,modifications and equivalents, which may be included within the spiritand scope of the invention as defined by the appended claims.

Furthermore, in the following description of embodiments of the presentinvention, numerous specific details are set forth in order to provide athorough understanding of the present invention. However, it should benoted that embodiments of the present invention may be practiced withoutthese specific details. In other instances, well known methods,procedures, and components have not been described in detail as not tounnecessarily obscure embodiments of the present invention.

Physical Description of Embodiments of the Present Invention for a BulkEraser

With reference to FIG. 1, in accordance with an embodiment of thepresent invention, a plan view of a hard-disk drive (HDD) 100manufactured with a tool, for example, a bulk eraser, for erasingrecorded information from a hard-disk drive is shown. FIG. 1 illustratesthe functional arrangement of component parts in HDD 100. The HDD 100includes at least one HGA 110 including a magnetic-recording head 110 a,for example, a perpendicular magnetic recording (PMR) head, a leadsuspension 110 c attached to the magnetic-recording head 110 a, and aload beam 110 d attached to a slider 110 b, which includes themagnetic-recording head 110 a at a distal end of the slider 110 b; theslider 110 b is attached at the distal end of the load beam 110 d to agimbal portion of the load beam 110 d. The HDD 100 also includes atleast one magnetic-recording disk 120, for example, a PMR disk,rotatably mounted on a spindle 126 and a drive motor (not shown, butwhose location is indicated by the crosshatching at the center of themagnetic-recording disk 120) attached to the spindle 126 for rotatingthe magnetic-recording disk 120. The magnetic-recording disk includes atleast one magnetic layer, which may include a structure including manythin-film layers including a thin-film layer of high coercivity magneticmaterial; the magnetic layer is deposited on a substrate, but need notbe in contact with the substrate, as other layers may be interposedbetween the substrate and the magnetic layer to provide the magneticlayer with suitable magnetic properties, such as magnetic anisotropy.The substrate may be composed of aluminum, an alloy of aluminum, aceramic, or glass. The drive motor includes a drive-motor stator and arotor; the rotor may include one or more drive-motor magnets which causethe rotor to rotate in response to a magnetic field generated by adrive-motor stator including motor windings; alternatively, thedrive-motor stator may include one or more drive-motor magnets whichcause the rotor to rotate in response to a magnetic field generated bymotor windings wound on the rotor. The magnetic-recording head 110 aincludes a write element, a so-called writer, a read element, aso-called reader, for respectively writing and reading informationstored on the magnetic-recording disk 120 of the HDD 100, and athermal-fly-height-control (TFC) element. The TFC element is configuredto position the read element of the magnetic-recording head 110 a incommunication with the magnetic-recording disk 120 for reading recordeddata from the magnetic-recording disk 120. The magnetic-recording disk120 or a plurality (not shown) of magnetic-recording disks may beaffixed to the spindle 126 with a disk clamp 128. If a plurality ofmagnetic-recording disks is provided, the plurality ofmagnetic-recording disks along with interposed spacers between themagnetic-recording disks is referred to by the term of art,“disk-stack”; however, as used herein, to simplify the discussion, theterm disk-stack will be also used to refer to a singlemagnetic-recording disk. The magnetic-recording disk 120 also has anoutside diameter (OD) 124 and an inside diameter (ID) 122. A radialdirection 174 of the magnetic-recording disk 120 is also shown in FIG. 1that is utilized in aligning the HDD in the bulk eraser for erasingrecorded information from the magnetic-recording disk 120. The HDD 100further includes an arm 132 attached to the HGA 110, a voice-coil motor(VCM) that includes an armature 136 including a voice-coil 140 attachedto the arm 132; and a VCM stator 144 including a voice-coil magnet (notshown); the armature 136 of the VCM, which is mounted on a pivot 148with an interposed pivot bearing 152, is attached to the arm 132 and isconfigured to move the arm 132 and the HGA 110 to access portions of themagnetic-recording disk 120.

With further reference to FIG. 1, in accordance with an embodiment ofthe present invention, electrical signals, for example, current to thevoice-coil 140 of the VCM, write signal to and read-back signal from themagnetic-recording head 110 a, are provided by a flexible cable 156.Interconnection between the flexible cable 156 and themagnetic-recording head 110 a may be provided by an arm-electronics (AE)module 160, which may have an on-board pre-amplifier for the read-backsignal, as well as other read-element-channel and write-element-channelelectronic components. The flexible cable 156 is coupled to anelectrical-connector block 164, which provides electrical communicationthrough electrical feedthroughs (not shown) provided by an HDD housing168. The HDD housing 168, also referred to as a casting, in conjunctionwith an HDD cover (not shown, as FIG. 1 shows the HDD 100 with the coverremoved) provides an enclosure, which is sealed and protects theinformation storage components of the HDD 100. The enclosure of the HDDalso has: a front side 102, a backside 104, a right side 106 and a leftside 108. As shown in FIG. 1, the view shown is onto the topside of theHDD with the cover removed. The bottom side of the HDD is not shown inFIG. 1, but a printed circuit board is mounted on the bottom side whichincludes electronic components used to control the access to themagnetic-recording disk 120 for writing recorded information to themagnetic-recording disk 120 or reading recorded information from themagnetic-recording disk 120.

With further reference to FIG. 1, in accordance with an embodiment ofthe present invention, other electronic components (not shown),including as a disk controller and servo-control electronics including adigital-signal processor (DSP), provide electrical signals to the drivemotor, the voice-coil 140 of the VCM and the magnetic-recording head 110a of the HGA 110. The electrical signal provided to the drive motorenables the drive motor to spin providing a torque to the spindle 126which is in turn transmitted to the magnetic-recording disk 120 that isaffixed to the spindle 126 by the disk clamp 128; as a result, themagnetic-recording disk 120 spins in a direction 172. The spinningmagnetic-recording disk 120 creates a cushion of air that acts as an airbearing on which the air-bearing surface (ABS) of the slider 110 b ridesso that the slider 110 b flies above the surface of themagnetic-recording disk 120 without making contact with a thinmagnetic-recording medium of the magnetic-recording disk 120 in whichinformation is recorded. The electrical signal provided to thevoice-coil 140 of the VCM enables the magnetic-recording head 110 a ofthe HGA 110 to access a data track 176 on which information is recorded.Thus, the armature 136 of the VCM swings through an arc 180, whichenables the HGA 110 attached to the armature 136 by the arm 132 toaccess various data tracks on the magnetic-recording disk 120.Information is stored on the magnetic-recording disk 120 in a pluralityof concentric data tracks (not shown) arranged in sectors on themagnetic-recording-head-facing side of the magnetic-recording disk 120,for example, sector 184. Correspondingly, each data track is composed ofa plurality of sectored data track portions, for example, sectored datatrack portion 188. Each sectored data track portion 188 is composed ofrecorded data and a header containing a servo-burst-signal pattern, forexample, an ABCD-servo-burst-signal pattern, information that identifiesthe data track 176, and error correction code information. In accessingthe data track 176, the read element of the magnetic-recording head 110a of the HGA 110 reads the servo-burst-signal pattern which providesinformation to the servo-control electronics, which controls theelectrical signal provided to the voice-coil 140 of the VCM, enablingthe magnetic-recording head 110 a to follow the data track 176. Uponfinding the data track 176 and identifying a particular sectored datatrack portion 188, the magnetic-recording head 110 a either reads databack from the data track 176 or writes data to the data track 176depending on instructions received by the disk controller from anexternal agent, for example, a microprocessor of a computer system.

With further reference to FIG. 1, in accordance with an embodiment ofthe present invention, a plan view of a head-arm-assembly (HAA) isshown. FIG. 1 illustrates the functional arrangement of the HAA withrespect to VCM and HGA 110. The HAA includes the HGA 110 and the arm132. The HAA is attached at the arm 132 to a carriage 134. In the caseof an HDD having multiple disks, or platters as disks are sometimesreferred to in the art, the carriage 134 is called an “E-block,” orcomb, because the carriage 134 is arranged to carry a ganged array ofarms that gives it the appearance of a comb. As shown in FIG. 1, thearmature 136 of the VCM is attached to the carriage 134 and thevoice-coil 140 is attached to the armature 136. The AE module 160 may beattached to the carriage 134 as shown. The carriage 134 is mounted onthe pivot 148 with the interposed pivot bearing 152, as previouslydescribed.

With reference now to FIG. 2A, in accordance with an embodiment of thepresent invention, a perspective view 200A of a bulk eraser 201 forerasing recorded information on a magnetic-recording disk, for example,magnetic-recording disk 120, in a HDD, for example, HDD 100, is shown.The bulk eraser 201 includes a plurality of magnets, for example, afirst magnet 210 and a second magnet 230, without limitation thereto, asembodiments of the present invention may include more than two magnetsor two sources of magnetic flux. The bulk eraser 201 includes astructure magnetically coupled with the plurality of magnets to producemagnetic-flux density in a gap, wherein the gap has a first portion 222,a second portion 224 and a third portion (not shown, but see descriptionof FIGS. 3A-3B). As used herein, it should be recognized that theGaussian system of units are used, so that a magnetic-flux density,known in the art as a magnetic induction field, or B-field, given inunits of Gauss, is equal to a magnetic field intensity, known in the artas a H-field, given in units of Oersteds, if the magnetization, known inthe art as a M-field, is negligible. Therefore, it should be understoodthat when referring to a magnetic-flux density, B-field, in a gap, themagnetic-flux density, B-field, in the gap is equivalent to anassociated magnetic field intensity, H-field, in the gap, which is awell-known convention in the art when using Gaussian units. In anembodiment of the present invention, as shown in FIG. 2A, the structuremay include: a yoke 270 including a first yoke portion 270 a and asecond yoke portion 270 b, a first pole piece 240, a second pole piece250 in the third pole piece 260. Two magnets, first magnet 210 andsecond magnet 230, are disposed with opposing polarity across the firstportion 222 of the gap. The direction 214 of the B-field, themagnetic-flux density, as well as the magnetization field, in the firstmagnet 210 is shown by the black arrow. The black arrow indicates that afirst end pole 212 proximate the first portion 222 of the gap has thepolarity of a south pole, and the end pole of the first magnet 210opposite the south pole has the polarity of a north pole. The blackarrow also indicates the direction of magnetic flux propagation throughthe first magnet 210. Similarly, the direction 234 of the B-field, themagnetic-flux density, as well as the magnetization field, in the secondmagnet 230 is shown by the white arrow. The white arrow indicates that asecond end pole 232 proximate first portion 222 of the gap has thepolarity of a south pole, and the end pole of the second magnet 230opposite the south pole has the polarity of a north pole. The whitearrow also indicates the direction of magnetic flux propagation throughthe second magnet 230. At least one of the plurality of magnets, forexample, magnets 210 and 230, may be a high-field-strength, permanentmagnet, which may be composed of a material such as neodymium ironboron, NdFeB. The grade of the NdFeB material used for at least onemagnet of the plurality of magnets may be a grade between about grade 48and about grade 54; however, a grade of about grade 50 provides a verystable magnet. The plurality of magnets 210 and 230 and the structureare configured to produce a magnetic-flux density in the second portion224 of the gap sufficient to erase recorded information from a portionof at least one magnetic-recording disk, for example, magnetic-recordingdisk 120, in a disk-stack of the HDD when the HDD is inserted into thesecond portion 224 of the gap. The plurality of magnets 210 and 230 andthe structure are configured to direct the magnetic-flux density in asubstantially radial direction, for example, radial direction 174, ofthe portion of the magnetic-recording disk in the HDD in the secondportion 224 of the gap. For example, the first pole piece 240 has afirst pole-tip portion 242, the second pole piece 250 has a secondpole-tip portion 252 and the third pole piece 260 has a third pole-tipportion 262 configured to provide magnetic-flux density in the secondportion 224 of the gap with the characteristics described above.

With further reference to FIG. 2A, in accordance with an embodiment ofthe present invention, the plurality of magnets, for example, magnets210 and 230, and the structure are configured to produce a magnetic-fluxdensity sufficient to erase recorded information from portions of aplurality of magnetic-recording disks in a disk-stack of the HDD, forexample, HDD 100. One type of recorded information that is frequentlyrequired to be erased in manufacturing is servo pattern information onthe magnetic-recording disk. Occasionally, it is found in themanufacturing process that the servo pattern is corrupted and it becomesnecessary to erase the corrupted servo pattern and to write a new servopattern to replace it. However, erasing the corrupted servo pattern byusing the magnetic recording heads can take a substantially long time,tens of minutes. The bulk eraser, for example, bulk eraser 201, cansubstantially reduce the erase time to tens of seconds. To accomplishthis, the HDD with the corrupted servo pattern is inserted into theerase field of the bulk eraser in a type of batch processing procedure,which erases several portions of the magnetic-recording disksimultaneously, which gives rise to the term of art “bulk eraser” todescribe the tool for erasing recorded information on amagnetic-recording disk of an HDD. Therefore, the plurality of magnetsare configured to produce a magnetic-flux density sufficient to eraserecorded information from a portion of at least one magnetic-recordingdisk containing servo information in a disk-stack of the HDD. Moreover,the bulk eraser can be used outside the scope of manufacturing, forexample, to erase recorded information, for example, data recorded by auser, from an HDD used in an in-service environment. Therefore, theplurality of magnets are configured to produce a magnetic-flux densitysufficient to erase recorded data from a portion of at least onemagnetic-recording disk containing recorded data in a disk-stack of theHDD to preserve security of the recorded data.

With further reference to FIG. 2A, in accordance with an embodiment ofthe present invention, another particularly useful application of thebulk eraser is for erasing magnetic-recording disks having highcoercivity, such as PMR disks. Thus, the plurality of magnets, forexample, magnets 210 and 230, and the structure may also be configuredto erase recorded information from a magnetic-recording disk that is aPMR disk. Moreover, the plurality of magnets and the structure areconfigured to produce magnetic-flux density such that magnetic-fluxdensity is applied to a localized portion of the magnetic-recording diskto suppress eddy currents in the magnetic-recording disk of the HDD.This allows for the magnetic-recording disk to be erased more quickly,because eddy currents can stall the drive motor preventing rotation ofthe magnetic-recording disk during the erasure process.

With further reference to FIG. 2A, in accordance with an embodiment ofthe present invention, another issue attending the use of the bulkeraser in the manufacturing process is that the erase fields used toerase recorded information on the magnetic-recording disk are fairlyhigh to overcome the coercivity of magnetic recording materials used inthe magnetic layer of the magnetic-recording disk. The magnetic momentin the drive-motor magnets can potentially be degraded when using thebulk eraser to erase recorded information on the magnetic-recordingdisk. Consequently, the magnetic-flux density produced by the pluralityof magnets and the structure is configured to erase recorded informationfrom the magnetic-recording disk disposed in the second portion of thegap without degrading the magnetization of a drive-motor magnet in thedrive motor disposed in the third portion of the gap. To assure that alarge portion of the magnetic-recording disk is erased without degradingthe magnetization of the drive-motor magnets, the intensity of a fieldcomponent of the magnetic-flux density directed along the radialdirection in the plane of the magnetic-recording disk produced by theplurality of magnets and the structure has a gradient as a function ofdistance along the radial direction at a transition region between thesecond portion of the gap and the third portion of the gap such that thegradient allows erasing recorded information from the magnetic-recordingdisk in close proximity to the drive-motor magnet in the drive motorwithout degrading the magnetization of the drive-motor magnet in thedrive motor. The high field gradient is also desirable, because itreduces the amount of time to erase portions of the magnetic-recordingdisk that cannot be reached by the erase field, for which it isnecessary to erase with a magnetic recording head; in other words, themore of the magnetic-recording disk that can be erased with the bulkeraser, the less of the magnetic-recording disk will have to be erasedby a magnetic recording head, which is a time-consuming process.Consequently, every additional millimeter along the radius of themagnetic-recording disk that can be erased by the erase field cansignificantly reduce the amount of time expended by erasing theremaining portions of the magnetic-recording disk with the magneticrecording head, which reduces the cost of manufacturing. Therefore, itis desirable to provide a bulk eraser with a strong erase field,magnetic-flux density, over the magnetic-recording disk and a steepgradient in the magnetic-flux density in the proximity to thedrive-motor magnet.

With reference now to FIG. 2B, in accordance with an embodiment of thepresent invention, a detailed perspective view 200B of a gap 202 of thebulk eraser 201 of FIG. 2A illustrating the configuration of thepole-tip portions 242, 252 and 262 at the gap 202 is shown. The bulkeraser 201 includes a first source of magnetic flux, for example, firstmagnet 210, disposed opposite a second source of magnetic flux, forexample, second magnet 230, across a first portion 222 of the gap 202.At least one of the first source of magnetic flux and the second sourceof magnetic flux produces sufficient magnetic-flux density in the secondportion 224 of the gap 202 to erase the magnetic-recording disk in theHDD. At least one of the first source of magnetic flux and the secondsource of magnetic flux may be an electromagnet. Alternatively, at leastone of the first source of magnetic flux and the second source ofmagnetic flux may be a high-field-strength, permanent magnet. The firstsource of magnetic flux may be a first magnet, for example, first magnet210, composed of the material NdFeB and the second source of magneticflux may be a second magnet, for example, second magnet 230, composed ofthe material NdFeB. The NdFeB material may have a grade between aboutgrade 48 and about grade 54; the NdFeB material may also have a grade ofabout grade 50.

With further reference to FIG. 2B, in accordance with an embodiment ofthe present invention, the first source has first end pole 212 disposedproximate the first portion 222 of the gap 202, and the second sourcehas a second end pole 232 disposed proximate the first portion 222 ofthe gap 202; the first and second end poles have 212 and 232 the samepolarity, for example, both are north poles, or alternatively, both aresouth poles. The bulk eraser 201 also includes: a first pole piece 240,which has a first pole-tip portion 242 and is disposed on the first endpole 212 in proximity to the first portion 222 of the gap 202; a secondpole piece 250, which has a second pole-tip portion 252 and is disposedon the second end pole 232 in proximity to the second portion 224 of thegap 202; and, a third pole piece 260, which has third pole-tip portion262 and is disposed proximate to the second portion 224 of the gap 202.The first pole-tip portion 242, the second pole-tip portion 252, and thethird pole-tip portion 262 define the second portion 224 of the gap 202that is located between the first pole-tip portion 242, the secondpole-tip portion 252, and the third pole-tip portion 262 and areconfigured such that magnetic-flux density in the second portion 224 ofthe gap 202 lies substantially parallel to a plane of themagnetic-recording disk, for example, magnetic-recording disk 120, toerase recorded information from a portion of the magnetic-recording diskwhen the HDD, for example, HDD 100, is inserted into the second portion224 of the gap 202. As used herein, the term “lies substantiallyparallel to a plane of the magnetic-recording disk” means that the planeof the magnetic-recording disk is aligned parallel to the plane of themagnetic-flux density within the manufacturing tolerances for insertingthe HDD 100 into the bulk eraser 201 and for providing magnetic-fluxdensity within the bulk eraser that is about oriented within a plane inthe second portion 224 of the gap 202.

With further reference to FIG. 2B, in accordance with an embodiment ofthe present invention, two trihedrals 204 and 206 are shown. Trihedral204 is located at the center of the front of the first portion 222 ofthe gap 202. Trihedral 204 includes three vectors 204 a, 204 b and 240 corthogonally disposed with respect to one another in a right-handedconfiguration. Vectors 204 a and 204 b lie in a plane disposed in thecenter of the gap 202 halfway between the first end pole 212 and thesecond end pole 232 and separates the top of the gap 202 from the bottomof the gap 202; the plane defined by the vectors 204 a and 204 b liessubstantially parallel to a plane of the magnetic-recording disk of theHDD when inserted into the gap to erase recorded information on themagnetic-recording disk. As used herein, the phrase “lies substantiallyparallel to a plane of the magnetic-recording disk” means about parallelwith the plane of the magnetic recording disk within the manufacturingtolerances for insertion of the HDD into the bulk eraser 201, and forfabricating a bulk eraser. Vectors 204 b and 204 c lie in a median planethat bisects the gap 202 into two symmetrical halves, a left half and aright half, when viewed from the front of the gap 202. Thus, vector 204b lies on a line down the center of the gap 202, which lies in asubstantially radial direction, for example, radial direction 174, ofthe portion of the magnetic-recording disk in the HDD when inserted intothe gap to erase recorded information on the magnetic-recording disk. Asused herein, the phrase “lies in a substantially radial direction” meansabout coincidently with the radial direction within the manufacturingtolerances for insertion of the HDD into the bulk eraser 201, and forfabricating a bulk eraser. Vector 204 c lies substantially perpendicularto the plane of the magnetic-recording disk of the HDD when insertedinto the gap to erase recorded information on the magnetic-recordingdisk and is about parallel to the direction of the axis of the spindleon which the disk-stack is mounted. As used herein, the phrase “liessubstantially perpendicular to the plane of the magnetic-recording disk”means about perpendicularly to the plane of the magnetic-recording diskwithin the manufacturing tolerances for insertion of the HDD into thebulk eraser 201, and for fabricating a bulk eraser. Vector 204 a liesperpendicular to the median plane defined by vectors 204 b and 204 c;vector 204 a and vector 204 c lie in a plane at the front of the gap202, which is parallel to the front side, for example, front side 102,of the HDD when inserted into the gap to erase recorded information onthe magnetic-recording disk. The distance that separates the front planeof the gap 202 defined by the vectors 204 a and 204 c from the frontside of the HDD is referred to by the term of art “stroke length,” whichis a measure of the distance that the HDD is inserted into the gap 202of the bulk eraser, for example, bulk eraser 201.

With further reference to FIG. 2B, in accordance with an embodiment ofthe present invention, trihedral 206 is similarly located at the centerof the front of the second portion 224 of the gap 202. Trihedral 206includes three vectors 206 a, 206 b and 240 c orthogonally disposed withrespect to one another in a right-handed configuration. Vectors 206 aand 206 b lie in the same plane as vectors 204 a and 204 b that isdisposed in the center of the gap 202 halfway between the first end pole212 and the second end pole 232 and separates the top of the gap 202from the bottom of the gap 202. Thus, the plane defined by the vectors206 a and 206 b also lies substantially parallel to a plane of themagnetic-recording disk of the HDD when inserted into the gap to eraserecorded information on the magnetic-recording disk. Vectors 206 b and206 c lie in the same plane as vectors 204 a and 204 b that is themedian plane that bisects the gap 202 into two symmetrical halves, aleft half and a right half, when viewed from the front of the gap 202.Thus, vector 206 b also lies on a line down the center of the gap 202,which lies in a substantially radial direction, for example, radialdirection 174, of the portion of the magnetic-recording disk in the HDDwhen inserted into the gap to erase recorded information on themagnetic-recording disk. Similar to vector 204 c, vector 206 c liessubstantially perpendicular to the plane of the magnetic-recording diskof the HDD when inserted into the gap to erase recorded information onthe magnetic-recording disk and is about parallel to the direction ofthe axis of the spindle on which the disk-stack is mounted. Vector 206 alies perpendicular to the median plane defined by vectors 206 b and 206c; vector 206 a and vector 206 c lie in a plane at the front of thesecond portion 224 of the gap 202 and in the back of the first portion222 of the gap 202, which is located about where the magnetic-fluxdensity becomes sufficient to erase recorded information from themagnetic-recording disk.

With further reference to FIG. 2B, in accordance with an embodiment ofthe present invention, the first pole-tip portion 242, the secondpole-tip portion 252, and the third pole-tip portion 262 are configuredsuch that the magnetic-flux density in the second portion 224 of the gap202 lies in a substantially radial direction, for example, radialdirection 174, of the portion of the magnetic-recording disk in the HDDfrom which recorded information is erased. The first pole-tip portion242, the second pole-tip portion 252, and the third pole-tip portion 262are configured to suppress magnetic-flux density in a third portion ofthe gap 202 such that the magnetization of the drive-motor magnet of thedrive motor in the HDD is not degraded when located within the thirdportion. The first pole-tip portion 242, the second pole-tip portion252, and the third pole-tip portion 262 are configured to confine themagnetic-flux density in the second portion 224 of the gap 202 to aregion of the magnetic-recording disk sufficiently localized such thatstrength of eddy currents in the magnetic-recording disk are suppressedwhen rotating the magnetic-recording disk to erase recorded informationon the magnetic-recording disk.

With further reference to FIG. 2B, in accordance with an embodiment ofthe present invention, the first pole-tip portion 242 may be configuredto direct magnetic flux emanating from the first pole-tip portion 242 tothe third pole-tip portion 262 and to concentrate magnetic-flux densityin the second portion 224 of the gap 202 substantially parallel to aplane of the magnetic-recording disk in the HDD in the second portion224 of the gap 202. For example, the first pole-tip portion 242 may betapered to concentrate magnetic-flux density in the second portion 224of the gap 202 substantially parallel to a plane of themagnetic-recording disk in the HDD in the second portion 224 of the gap202. The second pole-tip portion 252 may be configured to directmagnetic flux emanating from the second pole-tip portion 252 to thethird pole-tip portion 262 and to concentrate magnetic-flux density inthe second portion 224 of the gap 202 substantially parallel to a planeof the magnetic-recording disk in the HDD in the second portion of thegap. For example, the second pole-tip portion 252 may also be tapered toconcentrate magnetic-flux density in the second portion 224 of the gap202 substantially parallel to a plane of the magnetic-recording disk inthe HDD in the second portion 224 of the gap 202. The third pole-tipportion 262 may be configured to receive the magnetic flux emanatingfrom the first pole-tip portion 242 and the magnetic flux emanating fromthe second pole-tip portion 252 and to concentrate magnetic-flux densityin the second portion 224 of the gap 202 substantially parallel to aplane of the magnetic-recording disk in the HDD in the second portion224 of the gap 202.

With further reference to FIG. 2B, in accordance with an embodiment ofthe present invention, alternatively, the third pole-tip portion 262maybe configured to direct a second portion of magnetic flux emanatingfrom the third pole-tip portion 262 to the first pole-tip portion 242and to direct a second portion of magnetic flux emanating from the thirdpole-tip portion 262 to the second pole-tip portion 252 and toconcentrate magnetic-flux density in the second portion 224 of the gap202 substantially parallel to a plane of the magnetic-recording disk inthe HDD in the second portion 224 of the gap 202. The first pole-tipportion 242 may be configured to receive the second portion of magneticflux emanating from the third pole-tip portion 262 and to concentratemagnetic-flux density in the second portion 224 of the gap 202substantially parallel to a plane of the magnetic-recording disk in theHDD in the second portion 224 of the gap 202. For example, the firstpole-tip portion 242 may be tapered to concentrate magnetic-flux densityin the second portion 224 of the gap 202 substantially parallel to aplane of the magnetic-recording disk in the HDD in the second portion224 of the gap 202. The second pole-tip portion 252 may be configured toreceive the second portion of magnetic flux emanating from the thirdpole-tip portion 262 and to concentrate magnetic-flux density in thesecond portion 224 of the gap 202 substantially parallel to a plane ofthe magnetic-recording disk in the HDD in the second portion 224 of thegap 202. For example, the second pole-tip portion 252 may also betapered to concentrate magnetic-flux density in the second portion 224of the gap 202 substantially parallel to a plane of themagnetic-recording disk in the HDD in the second portion 224 of the gap202.

With further reference to FIG. 2A, in accordance with an embodiment ofthe present invention, the bulk eraser 201 further includes yoke 270having first yoke portion 270 a and second yoke portion 270 b. The firstyoke portion 270 a is magnetically coupled with the first source ofmagnetic flux, for example, first magnet 210, and the third pole piece260. The second yoke portion 270 b is magnetically coupled with thesecond source of magnetic flux, for example, second magnet 230, and thethird pole piece 260. The yoke 270 is configured to suppress straymagnetic flux and to increase magnetic-flux density in the secondportion 224 of the gap 202.

With further reference to FIGS. 1 and 2A-2B, in accordance with anembodiment of the present invention, the bulk eraser 201 may be used inmanufacturing of the HDD 100 to erase recorded information on themagnetic-recording disk 120. In manufacturing of the HDD 100, the bulkeraser 201 is provided that produces magnetic-flux density in a secondportion 224 of the gap 202 that is sufficient to erase recordedinformation on the magnetic-recording disk, for example,magnetic-recording disk 120. Also, a HDD, for example, HDD 100, isprovided; the HDD has an enclosure, a disk-stack having at least onemagnetic-recording disk 120 rotatably mounted on a spindle 126 and adrive motor; the drive motor has a rotor such that the rotor is attachedto the spindle for rotating the magnetic-recording disk 120 inside theenclosure. The plurality of magnets, for example, magnets 210 and 230,and a structure of the bulk eraser 201 are configured such thatmagnetic-flux density is oriented substantially parallel to a centralplane, defined by vectors 206 a and 206 b, in the second portion 224 ofthe gap 202 and in a substantially radial direction, for example, radialdirection 174, which is aligned with the vector 206 b, of a portion ofthe magnetic-recording disk 120 when the HDD 100 is inserted into thesecond portion 224 of the gap 202. The magnetic-recording disk 120 isrotated in the HDD 100. The HDD 100 is inserted into the second portion224 of the gap 202 of the bulk eraser 201 such that a plane of themagnetic-recording disk of the HDD is oriented substantially parallel tothe central plane, defined by vectors 206 a and 206 b, in second portion224 of the gap 202 such that magnetic-flux density is oriented in thesubstantially radial direction, for example, radial direction 174, whichis aligned with the vector 206 b, of the portion of themagnetic-recording disk. Consequently, the recorded information iserased from the portion of the magnetic-recording disk 120 in the HDD100 located in the second portion 224 of the gap 202. The HDD 100 maythen be removed from the second portion 224 of the gap 202.

With further reference to FIGS. 1 and 2A-2B, in accordance with anembodiment of the present invention, in using the bulk eraser 201 tomanufacture the HDD 100, the pole pieces 240, 250 and 260 of thestructure of the bulk eraser 201 and pole-tip portions 242, 252 in 262of the pole pieces 240, 250 and 260 are configured such thatmagnetic-flux density in the second portion 224 of the gap 202 isoriented substantially parallel to a central flux-propagation directionin the second portion 224 of the gap 202. When the HDD is inserted intothe second portion 224 of the gap 202 of the bulk eraser 201, themagnetic-recording disk 120 is oriented in the HDD 100 such that aradial direction 174 of a portion of the magnetic-recording disk 120 isoriented substantially parallel to the central flux-propagationdirection, for example, the direction of the vector 206 b, in the secondportion 224 of the gap 202. Also, upon inserting the HDD 100 into thesecond portion of the gap, the HDD 100 is inserted with an insertionspeed that is sufficient to assure complete erasure of recordedinformation on the magnetic-recording disk in the HDD 100. A sufficientinsertion speed into the gap 202 is less than or equal to 1 centimeterper second (cm/sec). When the HDD is removed from the second portion 224of the gap 202 of the bulk eraser 201, the HDD 100 is removed from thesecond portion 224 of the gap 202 with a removal speed that issufficient to assure complete erasure of recorded information on themagnetic-recording disk 120 in the HDD 100. A sufficient removal speedfrom the gap is less than or equal to 1 cm/sec.

With further reference to FIGS. 1 and 2A-2B, in accordance with anembodiment of the present invention, when the magnetic-recording disk120 is rotated in the HDD 100, the magnetic-recording disk 120 isrotated in the HDD with the drive motor at a rotation speed that issufficient to assure complete erasure of recorded information on themagnetic-recording disk 120 in the HDD 100 without stalling the drivemotor. A sufficient rotation speed of the magnetic-recording disk 120 isless than or equal to 2 Hertz (Hz). When rotating the magnetic-recordingdisk 120 in the HDD 100 with the drive motor, the drive motor is drivenby a low speed drive-motor-driver circuit on-board in the HDD 100 toprovide power to the drive motor to rotate the magnetic-recording disk120 at a slow speed to prevent stalling of the drive motor. Whenrotating the magnetic-recording disk in the HDD 100 with the drivemotor, power is provided to the low speed drive-motor-driver circuiton-board in the HDD 100. This power may be provided to the low speeddrive-motor-driver circuit on-board in the HDD 100 by attaching a cableand connector, attached to an external power supply, to the HDD 100.

With further reference to FIGS. 1 and 2A-2B, in accordance with anembodiment of the present invention, in using the bulk eraser 201 tomanufacture the HDD 100, the second portion 224 of the gap 202 isprovided with sufficient clearance to accommodate the HDD 100 uponinserting and removing the HDD 100 from the second portion 224 of thegap 202. A sufficient clearance of the second portion 224 of the gap 202may be less than or equal to about 2.6 centimeters (cm). Moreover, afixture may be provided for rapidly and reproducibly aligning the HDD100 in the second portion 224 of the gap 202. The fixture limits astroke length upon inserting the HDD 100 into the second portion 224 ofthe gap 202 such that the magnetic-flux density produced by theplurality of magnets, for example, magnets 210 in 230, and the structureis configured to erase recorded information from the portion of themagnetic-recording disk 120 disposed in the second portion 224 of thegap 202 without degrading the magnetization of a drive-motor magnet inthe drive motor disposed in a third portion of the gap 202. In addition,two magnets, for example, magnets 210 in 230, of the plurality ofmagnets are disposed with opposing polarity across the first portion 222of the gap 202; a separation between the two magnets of the plurality ofmagnets may be adjusted in the first portion 222 of the gap 202 suchthat the first portion 222 of the gap 202 has sufficient clearance toaccommodate the HDD 100 upon inserting and removing the HDD 100 from thesecond portion 224 of the gap 202 and the magnetic-flux density producedby the plurality of magnets and the structure is sufficient to eraserecorded information from a plurality of magnetic-recording disks of thedisk-stack when the HDD 100 is inserted into the second portion 224 ofthe gap 202.

Consequently, a HDD 100 manufactured using a bulk eraser 201 for erasingrecorded information on a magnetic-recording disk 120 in a HDD 100 lieswithin the spirit and scope of embodiments of the present invention. Inaccordance with embodiments of the present invention, the HDD 100includes at least one magnetic-recording disk 120 in a disk-stack of theHDD 100 from which recorded information has been erased by the bulkeraser 201. For example, in a re-work procedure of the manufacturingprocess the recorded information may be a first servo pattern erased bythe bulk eraser to prepare the magnetic-recording disk to write a secondservo pattern to replace the first servo pattern. Moreover, the recordedinformation may be recorded data on the magnetic-recording disk 120 inthe HDD 100, which is erased to preserve the security of the recordeddata.

With reference now to FIG. 3A, in accordance with an embodiment of thepresent invention, a plot 300A of the distribution 301 of magnetic-fluxdensity at the gap 202 of the bulk eraser 201 of FIGS. 2A and 2B isshown. FIG. 3A shows the distribution 301 of magnetic-flux density withrespect to a disk-stack, including magnetic-recording disks 320, 322,324 and 326, in a HDD, for example, HDD 100. The magnetic-recording disk326 at the top of the disk-stack may be identified with themagnetic-recording disk 120 of FIG. 1. The magnetic-flux density in thedistribution 301 is indicated by the magnitude and direction of thearrows shown in FIG. 3A, for example, the magnetic-flux-density vector310. The plane of FIG. 3A coincides with the median plane defined byvectors 206 b and 206 c and defined by vectors 204 b and 204 c of FIG.2B. The traces of several planes are indicated, which serve to show thevarious portions of the gap 202. The trace of the plane 3B-3Bcorresponds to a plane parallel to the plane of the magnetic-recordingdisk 324; the plane 3B-3B also corresponds to the plane of the FIG. 3B,subsequently described. The trace of plane A-A indicated by a dashedline coincides with the plane at the front of the second portion 224 ofthe gap 202 and in the back of the first portion 222 of the gap 202, inwhich vector 206 a and vector 206 c lie as shown in FIG. 2A. The traceof plane B-B indicated by a dashed line coincides with the plane at thefront of the first portion 222 of the gap 202, in which vector 204 a andvector 204 c lie as shown in FIG. 2A. Thus, the first portion 222 of thegap 202 lies between the plane A-A and the plane B-B; the first portion222 of the gap 202 lies between the outer surfaces of the first polepiece 240 in the second pole piece 250; these outer surfaces areindicated by the arrow-heads of the vertical arrow indicating thelocation of the first portion 222 of the gap 202, which coincide withthe boundaries of a relatively feel free area shown at the center ofFIG. 3A. The trace of plane C-C indicated by a dashed line coincideswith the plane in the back of the second portion 224 of the gap 202,which lies at the face of the third pole-tip portion 262. Thus, thesecond portion 224 of the gap 202, indicated by the double headed arrow,lies between the plane A-A and the plane C-C. As shown in FIG. 3A, thedistribution 301 of magnetic-flux density in the second portion 224 ofthe gap 202 is intense as indicated by the magnitude and crowding of thearrows associated with the magnetic-flux-density vectors. As shown inFIG. 3A, magnetic-flux density in the second portion 224 of the gap 202defined by first pole-tip portion 242, the second pole-tip portion 252,and the third pole-tip portion 262 and located between the firstpole-tip portion 242, the second pole-tip portion 252, and the thirdpole-tip portion 262 lies substantially parallel to a plane of themagnetic-recording disk, for example, to plane 3B-3B of themagnetic-recording disks 324, as well as to each of the planes of theremaining magnetic-recording disks 320, 324 and 326 of the disk-stack,to erase recorded information from a portion of the magnetic-recordingdisk when the HDD, for example, HDD 100, is inserted into the secondportion 224 of the gap 202.

With further reference to FIG. 3A and as shown therein, in accordancewith an embodiment of the present invention, the end poles 212 and 232of the first magnet 210 and the second magnet 230 are south poles sothat the magnetic-flux-density vectors are directed towards the firstpole-tip portion 242 and the second pole-tip portion 252 from the thirdpole-tip portion 262. Thus, the third pole-tip portion 262 is configuredto direct a first portion of magnetic flux emanating from the thirdpole-tip portion 262 to the first pole-tip portion 242 and to direct asecond portion of magnetic flux emanating from the third pole-tipportion 262 to the second pole-tip portion 252 and to concentratemagnetic-flux density in the second portion 222 of the gap 202substantially parallel to a plane of the magnetic-recording disk, forexample, to plane 3B-3B of the magnetic-recording disks 324, in the HDDin the second portion 222 of the gap 202. The first pole-tip portion 242is configured to receive the first portion of magnetic flux emanatingfrom the third pole-tip portion 262 and to concentrate magnetic-fluxdensity in the second portion 224 of the gap 202 substantially parallelto a plane of the magnetic-recording disk, for example, each of themagnetic-recording disks 320, 322, 324 and 326 of the disk-stack, in theHDD 100 in the second portion 224 of the gap 202. The second pole-tipportion 252 is configured to receive the second portion of magnetic fluxemanating from the third pole-tip portion 262 and to concentratemagnetic-flux density in the second portion 224 of the gap 202substantially parallel to a plane of the magnetic-recording disk, forexample, to plane 3B-3B of the magnetic-recording disks 324, in the HDD100 in the second portion 224 of the gap 202.

Alternatively, the end poles 212 and 232 of the first magnet 210 and thesecond magnet 230 may be north poles so that the magnetic-flux-densityvectors are directed towards the third pole-tip portion 262 from thefirst pole-tip portion 242 and the second pole-tip portion 252. Thus,the first pole-tip portion 242 may be configured to direct magnetic fluxemanating from the first pole-tip portion 242 to the third pole-tipportion 262 and to concentrate magnetic-flux density in the secondportion 224 of the gap 202 substantially parallel to a plane of themagnetic-recording disk, for example, to plane 3B-3B of themagnetic-recording disks 324, in the HDD 100 in the second portion 224of the gap 202. The second pole-tip portion 252 may be configured todirect magnetic flux emanating from the second pole-tip portion 252 tothe third pole-tip portion 262 and to concentrate magnetic-flux densityin the second portion 224 of the gap 202 substantially parallel to aplane of the magnetic-recording disk, for example, each of themagnetic-recording disks 320, 322, 324 and 326 of the disk-stack, in theHDD 100 in the second portion 224 of the gap 202. The third pole-tipportion 262 may be configured to receive the magnetic flux emanatingfrom the first pole-tip portion 242 and the magnetic flux emanating fromthe second pole-tip portion 252 and to concentrate magnetic-flux densityin the second portion 224 of the gap 202 substantially parallel to aplane of the magnetic-recording disk, for example, to plane 3B-3B of themagnetic-recording disks 324, in the HDD 100 in the second portion 224of the gap 202.

With further reference to FIG. 3A, in accordance with an embodiment ofthe present invention, the trace of plane D-D indicated by a dashed linecoincides with a plane tangent to the surface of a drive-motor magnet330 proximate to the second portion 224 of the gap 202. The trace ofplane E-E indicated by a dashed line coincides with a plane tangent tothe surface of a drive-motor magnet 334 proximate to the front of thefirst portion 222 of the gap 202. The space in the first portion 222 ofthe gap 202 between the front of the first portion 222 of the gap 202,plane B-B, and plane D-D defines the third portion 340 of the gap 202.The magnetic-flux density produced by the plurality of magnets and thestructure is configured to erase recorded information from themagnetic-recording disk disposed in the second portion 224 of the gap202 without degrading the magnetization of a drive-motor magnet, forexample, drive-motor magnet 330 and drive-motor magnet 334, in the drivemotor disposed in the third portion 340 of the gap 202. Moreover, thefirst pole-tip portion 242, the second pole-tip portion 252, and thethird pole-tip portion 262 are configured to suppress magnetic-fluxdensity in a third portion 340 of the gap 202 such that themagnetization of the drive-motor magnet, for example, drive-motor magnet330 and drive-motor magnet 334, of the drive motor in the HDD is notdegraded when located within the third portion 340. The trace of planeF-F indicated by a dashed line coincides with the front side 102 of theHDD 100. The stroke length 342 is the distance between the plane F-F andthe plane B-B indicated by the double headed arrow labeled 342 anddetermines the maximum safe distance that the HDD 100 can be insertedinto the gap 202 without erasing the drive-motor magnets, for example,drive-motor magnet 330 and drive-motor magnet 334.

With reference now to FIG. 3B, in accordance with an embodiment of thepresent invention, a plot 300B of the distribution 302 of magnetic-fluxdensity and contours 360, 362, 364, 368 and 370 of constant magnitude ofmagnetic-flux density in the plane 3B-3B of one magnetic-recording disk324 of the disk-stack of FIG. 3A is shown. In contrast with FIG. 3A, themagnetic-flux-density vectors are directed towards the third pole-tipportion 262, as for the case when the first end pole 212 and the secondend pole 232 are north poles instead of the south poles as for FIGS. 2A,2B and 3A; this change of polarity is of little consequence for thedescription, as the bulk eraser 201 can work with end poles of eitherpolarity are previously described, as long as the end poles 212 and 232have the same polarity. FIG. 3B shows a portion of the disk wherein themagnetic-flux density is sufficient to erase recorded information. Themagnetic-flux density in the distribution 302 is indicated by themagnitude and direction of the arrows shown in FIG. 3A, for example, themagnetic-flux-density vector 312. The plane of FIG. 3A coincides withthe plane 3B-3B of the magnetic-recording disk 324 of FIG. 3A. Severalcontours 360, 362, 364, 368 and 370 of constant magnitude ofmagnetic-flux density are indicated. The traces of several planes, forexample, planes A-A, B-B, C-C, D-D, E-E and F-F, are indicated, whichserve to identify the various portions of the gap 202 as previouslydescribed for FIG. 3B. The magnetic-recording disc 324 has a radialdirection 350, an OD track 354 and an ID track 352. The outside diameter338 of the drive motor is shown as the drive motor is disposed in thegap 202 of the bulk eraser 201. Contours closer to the trace of planeC-C, which lies at the face of the third pole-tip portion 262,correspond to magnetic-flux-density vectors that have greater magnitude.For example, contour 360 has the greatest magnitude and contour 368 hasthe least magnitude; this is also indicated by the density ofmagnetic-flux-density vectors located within the contour; for example,contour 368 shows virtually no magnetic-flux density vectors ofmeasurable magnitude. The contour 370 corresponds to a magnetic-fluxdensity sufficient to erase a portion of the magnetic-recording disk324; the portion of the magnetic-recording disk 324 that lies betweencontour 370 and the outside perimeter of the magnetic-recording disk 324defines the portion of the magnetic-recording disk 324 where themagnetic-flux density is sufficient to erase recorded information on themagnetic-recording disk 324 in the disk-stack of the HDD 100.

With further reference to FIG. 3B, in accordance with an embodiment ofthe present invention, the magnetic-flux-density vectors in the portionof the magnetic-recording disk where the magnetic-flux density issufficient to erase recorded information are such that the magnetic-fluxdensity in the second portion 224 of the gap 202 lies in thesubstantially radial direction 350 of the portion of themagnetic-recording disk 324 in the HDD 100. As used herein, the phrase“lies in the substantially radial direction” means that the directionsof the magnetic-flux-density vectors are aligned as a whole as parallelas to the radial direction as can be obtained within manufacturingtolerances. Because an individual magnetic-flux-density vector maydeviate from the radial direction 350 and the magnetic-flux-densityvectors are symmetrically disposed about the radial direction 350, onthe average, the deviations of all the magnetic-flux-density vectors inthe second portion 224 of the gap 202 from the radial direction 350 isabout zero, when the magnetic-flux density in the second portion 224 ofthe gap 202 lies in the substantially radial direction 350 of theportion of the magnetic-recording disk 324. The stroke length 342 isalso shown indicating the relative disposition of the HDD 100 in thedistribution 302 of the magnetic-flux density in the gap 202 of the bulkeraser 201. As the plane 3B-3B does not coincide with plane disposed inthe center of the gap 202 halfway between the first end pole 212 and thesecond end pole 232, which separates the top of the gap 202 from thebottom of the gap 202, defined by the vectors 204 a and 204 b andvectors 206 a and 20 b of FIG. 2B, the corresponding projection vectorsof these vectors onto the plane 3B-3B are shown: vectors 304 a and 304 band vectors 306 a and 306 b, respectively. Therefore, vectors 304 a and306 a lie in the same median plane as vectors 204 a and 206 a thatbisects the gap 202 into two symmetrical halves, a left half and a righthalf, when viewed from the front of the gap 202. As the median plane ofthe bulk eraser is located at a central portion of the gap it contains acentral flux-propagation direction for each disk in the disk-stack; aradial direction 350 of a portion of the magnetic-recording disk 324 isoriented substantially parallel to the central flux-propagationdirection, for example, the direction of the vector 306 b, in the secondportion 224 of the gap 202. Even though the magnetic-recording disk hasa plurality of radial directions, a radial direction of a portion of themagnetic-recording disk, as used herein, refers to a radial directionsubstantially aligned within the median plane of the bulk eraser asshown in FIG. 3B. Therefore, such a radial direction, as used herein,may provide a maximum stroke length that precludes erasure of adrive-motor magnet, yet allows the greatest portion of amagnetic-recording disk to be disposed within a portion of thedistribution of magnetic-flux density sufficient to erase the portion ofthe magnetic-recording disk.

With further reference to FIG. 3B, in accordance with an embodiment ofthe present invention, the plurality of magnets, for example, magnets210 in 230, and the structure are configured to direct the magnetic-fluxdensity in a substantially radial direction, for example, radialdirection 350, of the portion of the magnetic-recording disk, forexample, magnetic-recording disk 324, in the HDD 100 in the secondportion 224 of the gap 202. The intensity of a field component of themagnetic-flux density directed along the radial direction, for example,radial direction 350, in the plane of the magnetic-recording disk, forexample, magnetic-recording disk 324, produced by the plurality ofmagnets and the structure has a gradient as a function of distance alongthe radial direction, for example, radial direction 350, at a transitionregion between the second portion 224 of the gap 202 and the thirdportion 340 of the gap 202 such that the gradient allows erasingrecorded information from the magnetic-recording disk in close proximityto the drive-motor magnet in the drive motor, for example, indicated bythe outside diameter 338 of the drive motor, without degrading themagnetization of the drive-motor magnet, for example, drive-motormagnets 330 in 334, in the drive motor. As shown in FIG. 3B, thetransition region lies substantially within the first portion 222 of thegap 202 between plane A-A and plane D-D; however, as shown in FIG. 3Bthe transition region may extend from plane A-A somewhat into the secondportion 224 of the gap 202 to the contour 370 corresponding tomagnetic-flux density sufficient to erase a portion of themagnetic-recording disk, for example, magnetic-recording disk 324.Moreover, the first pole-tip portion 242, the second pole-tip portion252, and the third pole-tip portion 262 are configured such that themagnetic-flux density in the second portion 224 of the gap 202 lies in asubstantially radial direction, for example, radial direction 350, ofthe portion of the magnetic-recording disk, for example,magnetic-recording disk 324, in the HDD 100, which is indicated by thenumerous magnetic-flux-density vectors lying parallel to the radialdirection 350 in FIG. 3B. Moreover, the plurality of magnets, forexample, magnets 210 in 230, and the structure are configured to producethe magnetic-flux density such that the magnetic-flux density is appliedto a localized portion of the magnetic-recording disk, for example, theportion, without limitation thereto, of the magnetic-recording disk 324that lies between contour 370 and the outside perimeter of themagnetic-recording disk 324, to suppress eddy currents in themagnetic-recording disk, for example, magnetic-recording disk 324, ofthe HDD 100.

Physical Description of Embodiments of the Present Invention for a BulkEraser Including at Least Three Magnets Configured for Erasing RecordedInformation

With reference now to FIG. 4A, in accordance with an embodiment of thepresent invention, a perspective view 400A of an alternative embodimentof a bulk eraser 401 is shown. FIG. 4A shows at least three magnets 410,430 and 460 and a structure magnetically coupled with the at least threemagnets 410, 430 and 460 to produce magnetic-flux density in a gapsufficient to erase recorded information from a portion of themagnetic-recording disk, for example, magnetic-recording disk 120, in adisk-stack of the HDD, for example, HDD 100. The bulk eraser 401includes at least three magnets 410, 430 and 460 and a structuremagnetically coupled with the at least three magnets 410, 430 and 460 toproduce magnetic-flux density in a gap. In one embodiment of the presentinvention, as shown in FIG. 4A, the structure may include a yoke 480including a first yoke portion 470 a and a second yoke portion 470 b, afirst shield 440, a second shield 450 and a pole piece 470 having athird pole-tip portion 472. The first magnet 410 has a first pole-tipportion 416; the second magnet 430 has a second pole-tip portion 436;and the pole piece 470 has a third pole-tip portion 472, all of whichserve to produce magnetic-flux density in a gap. The gap, similar to gap202 of FIGS. 2A and 2B, has a first portion 422, a second portion 424and a third portion, similar to third portion 340 of FIGS. 3A and 3B.The first magnet 410 and a second magnet 430 are disposed with opposingend poles 412 and 432, respectively, of the same polarity across thefirst portion 422 of the gap. The direction 414 of the B-field, themagnetic-flux density, as well as the magnetization field, in the firstmagnet 410 is shown by the upper arrow. The upper arrow indicates that afirst end pole 412 proximate the first portion 422 of the gap has thepolarity of a north pole, and the end pole of the first magnet 410opposite the north pole has the polarity of a south pole. The arrow alsoindicates the direction of magnetic flux propagation through the firstmagnet 410. Similarly, the direction 434 of the B-field, themagnetic-flux density, as well as the magnetization field, in the secondmagnet 430 is shown by the lower arrow. The lower arrow indicates that asecond end pole 432 proximate first portion 422 of the gap has thepolarity of a north pole, and the end pole of the second magnet 430opposite the north pole has the polarity of a south pole. The arrow alsoindicates the direction of magnetic flux propagation through the secondmagnet 430. The direction 464 of the B-field, the magnetic-flux density,as well as the magnetization field, in the third magnet 460 is shown bythe horizontal arrow. The horizontal arrow indicates that a third endpole 462 proximate the first portion 422 of the gap has the polarity ofa south pole, and the end pole of the third magnet 460 opposite thesouth pole has the polarity of a north pole. The arrow also indicatesthe direction of magnetic flux propagation through the first magnet 460.

With further reference to FIG. 4A, in accordance with an embodiment ofthe present invention, at least one of the at least three magnets 410,430 and 460 may be a high-field-strength, permanent magnet, which may becomposed of a material such as neodymium iron boron, NdFeB. The grade ofthe NdFeB material used for at least one magnet of the three magnets410, 430 and 460 may have a grade between about grade 48 and about grade54; however, a grade of about grade 50 provides a very stable magnet.The at least three magnets 410, 430 and 460 and the structure areconfigured to produce a magnetic-flux density in the second portion 424of the gap sufficient to erase recorded information from a portion of atleast one magnetic-recording disk, for example, magnetic-recording disk120, in a disk-stack of the HDD 100 when the HDD 100 is inserted intothe second portion 424 of the gap. The at least three magnets 410, 430and 460 and the structure are configured to direct the magnetic-fluxdensity in a substantially radial direction of the portion of themagnetic-recording disk, similar to radial direction 350 of themagnetic-recording disk 324 of FIG. 3B as previously described, in theHDD 100 in the second portion 424 of the gap.

With further reference to FIG. 4A and as previously described in FIGS.3A and 3B for similar embodiments of the present invention, inaccordance with an embodiment of the present invention, the third magnet460 is disposed across the second portion 424 of the gap opposite thefirst magnet 410 and the second magnet 430 with a end pole of the thirdmagnet 462 of opposite polarity to the end poles 412 and 432 of thefirst magnet 410 and the second magnet 430, respectively. The at leastthree magnets 410, 430 and 460 and the structure are configured toproduce a magnetic-flux density sufficient to erase recorded informationfrom portions of a plurality of magnetic-recording disks, for example,similar to disks 320, 322, 324 in 326 as previously described for FIG.3A, in a disk-stack of the HDD 100. The at least three magnets 410, 430and 460 and the structure are configured to produce the magnetic-fluxdensity such that the magnetic-flux density is applied to a localizedportion of the magnetic-recording disk to suppress eddy currents in themagnetic-recording disk of the HDD 100, as previously described above.The magnetic-flux density produced by the at least three magnets 410,430 and 460 and the structure is configured to erase recordedinformation from the magnetic-recording disk, for example, similar tomagnetic-recording disk 324, disposed in the second portion 424 of thegap without degrading the magnetization of a drive-motor magnet, forexample, similar to drive-motor magnets 330 and 334, in the drive motordisposed in the third portion of the gap, for example, similar to thethird portion 340 described above for FIGS. 3A and 3B. The intensity ofa field component of the magnetic-flux density directed along the radialdirection, for example, similar to radial direction 350, in the plane ofthe magnetic-recording disk, for example, similar to magnetic-recordingdisk 324, produced by the at least three magnets 410, 430 and 460 andthe structure has a gradient as a function of distance along the radialdirection at a transition region, similar to the transition regiondescribed above for FIG. 3B, between the second portion 424 of the gapand the third portion, for example, similar to the third portion 340described above for FIGS. 3A and 3B, of the gap such that the gradientallows erasing recorded information from the magnetic-recording disk inclose proximity to the drive-motor magnet, for example, similar todrive-motor magnets 330 and 334, in the drive motor without degradingthe magnetization of the drive-motor magnet in the drive motor.

With reference now to FIGS. 4B and 4C, in accordance with an embodimentof the present invention, an elevation view 400B of a left side and anelevation view 400C of a front side of the bulk eraser 401 of FIG. 4Aare shown. The bulk eraser 401 includes a first magnet 410 disposedopposite a second magnet 430 across a first portion 422 of a gap, forexample, similar to gap 202 shown in FIG. 2A. The first magnet 410 hasfirst end pole 412 disposed proximate the first portion 422 of the gapand first pole-tip portion 416 disposed proximate the second portion 424of the gap. The second magnet 430 has the second end pole 432 disposedproximate the first portion 422 of the gap and second pole-tip portion436 disposed proximate the second portion 424 of the gap. The first andsecond end poles 412 and 432 have same polarity, as described above. Thebulk eraser 401 also includes a first magnetic shield 440, which isdisposed on the first end pole 412 in proximity to the first portion 422of the gap, and a second magnetic shield 450, which is disposed on thesecond end pole 432 in proximity to the first portion 422 of the gap.The bulk eraser 401 also includes a third magnet 460, which is disposedproximate to the second portion 424 of the gap. The third magnet 460 hasa third end pole 462, which is disposed proximate the second portion 424of the gap. The third end pole 462 has a polarity opposite to the firstand second end poles 412 and 432. The bulk eraser 401 also includes thepole piece 470, which is disposed on the third end pole 462 in proximityto the second portion 424 of the gap. The pole piece 470 has a thirdpole-tip portion 472. The first pole-tip portion 416, the secondpole-tip portion 436, and the third pole-tip portion 472 define a secondportion 424 of the gap located between the first pole-tip portion 416,the second pole-tip portion 436, and the third pole-tip portion 472 andare configured such that magnetic-flux density in the second portion 424of the gap lies substantially parallel to a plane of themagnetic-recording disk, for example, similar to plane 3B-3B of themagnetic-recording disks 324 as shown in FIG. 3B, in a disk-stack of thehard-disk drive to erase recorded information from a portion on themagnetic-recording disk, for example, similar to the portion of themagnetic-recording disk 324 that lies between contour 370 and theoutside perimeter of the magnetic-recording disk 324 as shown in FIG.3B, when the hard-disk drive is inserted into the second portion 424 ofthe gap. The first pole-tip portion 416, the second pole-tip portion436, and the third pole-tip portion 472 are configured such that themagnetic-flux density in the second portion 424 of the gap lies in asubstantially radial direction, for example, similar to radial direction350 as shown in FIG. 3B, of the portion of the magnetic-recording diskof the hard-disk drive. The first pole-tip portion 416, the secondpole-tip portion 436, and the third pole-tip portion 472 are configuredto suppress magnetic-flux density in a third portion of the gap, forexample, similar to the third portion 340 described above for FIGS. 3Aand 3B, such that the magnetization of the drive-motor magnet of thedrive motor in the hard-disk drive is not degraded when located withinthe third portion.

With further reference to FIGS. 4B and 4C, in accordance with anembodiment of the present invention, the end poles 412 and 432 of thefirst magnet 410 and the second magnet 430 are north poles so that themagnetic-flux-density vectors are directed towards the third pole-tipportion 472 from the first pole-tip portion 416 and the second pole-tipportion 436. Thus, the first pole-tip portion 416 is configured todirect magnetic flux emanating from the first pole-tip portion 416 tothe third pole-tip portion 472 and to concentrate magnetic-flux densityin the second portion 424 of the gap, similar to gap 202 shown in FIG.2B, substantially parallel to a plane of the magnetic-recording disk,for example, similar to plane 3B-3B of the magnetic-recording disks 324,in the HDD 100 in the second portion 424 of the gap. The second pole-tipportion 436 is configured to direct magnetic flux emanating from thesecond pole-tip portion 436 to the third pole-tip portion 472 and toconcentrate magnetic-flux density in the second portion 424 of the gapsubstantially parallel to a plane of the magnetic-recording disk, forexample, similar to each of the magnetic-recording disks 320, 322, 324and 326 of the disk-stack shown in FIG. 3A, in the HDD 100 in the secondportion 424 of the gap. The third pole-tip portion 472 is configured toreceive the magnetic flux emanating from the first pole-tip portion 416and the magnetic flux emanating from the second pole-tip portion 436 andto concentrate magnetic-flux density in the second portion 424 of thegap substantially parallel to a plane of the magnetic-recording disk,for example, similar to plane 3B-3B of the magnetic-recording disks 324,in the HDD 100 in the second portion 424 of the gap.

Alternatively, the end poles 412 and 432 of the first magnet 410 and thesecond magnet 430 may be south poles so that the magnetic-flux-densityvectors are directed towards the first pole-tip portion 416 and thesecond pole-tip portion 436 from the third pole-tip portion 472. Thus,the third pole-tip portion 472 may be configured to direct a firstportion of magnetic flux emanating from the third pole-tip portion 472to the first pole-tip portion 416 and to direct a second portion ofmagnetic flux emanating from the third pole-tip portion 472 to thesecond pole-tip portion 436 and to concentrate magnetic-flux density inthe second portion 222 of the gap, similar to gap 202 shown in FIG. 2B,substantially parallel to a plane of the magnetic-recording disk, forexample, similar to plane 3B-3B of the magnetic-recording disks 324, inthe HDD in the second portion 222 of the gap. The first pole-tip portion416 may be configured to receive the first portion of magnetic fluxemanating from the third pole-tip portion 472 and to concentratemagnetic-flux density in the second portion 424 of the gap substantiallyparallel to a plane of the magnetic-recording disk, for example, similarto each of the magnetic-recording disks 320, 322, 324 and 326 of thedisk-stack shown in FIG. 3A, in the HDD 100 in the second portion 424 ofthe gap. The second pole-tip portion 436 may be configured to receivethe second portion of magnetic flux emanating from the third pole-tipportion 472 and to concentrate magnetic-flux density in the secondportion 424 of the gap substantially parallel to a plane of themagnetic-recording disk, for example, similar to plane 3B-3B of themagnetic-recording disks 324, in the HDD 100 in the second portion 424of the gap.

With further reference to FIGS. 4B and 4C, in accordance with anembodiment of the present invention, the pole piece 470 is shaped toconcentrate magnetic-flux density in the second portion 424 of the gapsubstantially parallel to the plane of the magnetic-recording disk, forexample, similar to magnetic-recording disk 324 shown in FIG. 3B, in thedisk-stack of the hard-disk drive in the second portion 424 of the gap.The bulk eraser 401 further includes a yoke 480 having a first yokeportion 480 a and a second yoke portion 480 b. The first yoke portion480 a is magnetically coupled with the first magnet 410, the thirdmagnet 460 and the pole piece 470. The second yoke portion 480 b ismagnetically coupled with the second magnet 430, the third magnet 460and the pole piece 470. The yoke 480 is configured to suppress straymagnetic flux and to increase magnetic-flux density in the secondportion 424 of the gap. Alternative embodiments of the present inventionfor the yoke that provide further suppression of stray magnetic flux andfurther increase the magnetic-flux density in the second portion 424 ofthe gap are shown in FIG. 5 and are next described.

With reference now to FIG. 5, in accordance with an embodiment of thepresent invention, a perspective view 500 of an alternative embodimentof a bulk eraser 501 is shown. The bulk eraser 501 includes sevenmagnets 510, 530, 560, 582, 586, 592 and 596 and a structuremagnetically coupled with the seven magnets 510, 530, 560, 582, 586, 592and 596 to produce magnetic-flux density in a gap sufficient to eraserecorded information from a portion of the magnetic-recording disk, forexample, magnetic-recording disk 120, in a disk-stack of the HDD, forexample, HDD 100. The bulk eraser 501 includes a first magnet 510disposed opposite a second magnet 530 across a first portion 522 of agap, for example, similar to gap 202 shown in FIG. 2A. The first magnet510 has a first end pole 512 disposed proximate the first portion 522 ofthe gap and a first pole-tip portion 516 disposed proximate a secondportion 524 of the gap. The second magnet 530 has a second end pole 532disposed proximate the first portion 522 of the gap and a secondpole-tip portion 536 disposed proximate the second portion 524 of thegap. The first and second end poles 512 and 532 have same polarity. Thedirection 514 of the B-field, the magnetic-flux density, as well as themagnetization field, in the first magnet 510 is shown by the upper arrowin the right leg of the first yoke portion 580 a. The upper arrowindicates that a first end pole 512 proximate the first portion 522 ofthe gap has the polarity of a north pole, and the end pole of the firstmagnet 510 opposite the north pole has the polarity of a south pole. Thearrow also indicates the direction of magnetic flux propagation throughthe first magnet 510. Similarly, the direction 534 of the B-field, themagnetic-flux density, as well as the magnetization field, in the secondmagnet 530 is shown by the lower arrow in the right leg of the secondyoke portion 580 b. The lower arrow indicates that a second end pole 532proximate first portion 522 of the gap has the polarity of a north pole,and the end pole of the second magnet 530 opposite the north pole hasthe polarity of a south pole. The arrow also indicates the direction ofmagnetic flux propagation through the second magnet 530. The direction564 of the B-field, the magnetic-flux density, as well as themagnetization field, in the third magnet 560 is shown by the horizontalarrow at the middle of the yoke 580. The horizontal arrow indicates thata third end pole 562 proximate the first portion 522 of the gap has thepolarity of a south pole, and the end pole of the third magnet 560opposite the south pole has the polarity of a north pole. The arrow alsoindicates the direction of magnetic flux propagation through the thirdmagnet 560.

With further reference to FIG. 5, in accordance with an embodiment ofthe present invention, the bulk eraser 501 also includes a firstmagnetic shield 540, which is disposed on the first end pole 512 inproximity to the first portion 522 of the gap, and a second magneticshield 550, which is disposed on the second end pole 532 in proximity tothe first portion 522 of the gap. The bulk eraser 501 also includes athird magnet 560, which is disposed proximate to a second portion 524 ofthe gap. The third magnet 560 has a third end pole 562, which isdisposed proximate the second portion 524 of the gap. The third end pole562 has a polarity opposite to the first and second end poles 512 and532. The bulk eraser 501 also includes a pole piece 570, which isdisposed on the third end pole 562 in proximity to the second portion524 of the gap. The pole piece 570 has a third pole-tip portion 572. Thefirst pole-tip portion 516, the second pole-tip portion 536, and thethird pole-tip portion 572 define a second portion 524 of the gaplocated between the first pole-tip portion 516, the second pole-tipportion 536, and the third pole-tip portion 572 and are configured suchthat magnetic-flux density in the second portion 524 of the gap liessubstantially parallel to a plane of the magnetic-recording disk, forexample, similar to plane 3B-3B of the magnetic-recording disks 324 asshown in FIG. 3B, in a disk-stack of the hard-disk drive to eraserecorded information from a portion on the magnetic-recording disk, forexample, similar to the portion of the magnetic-recording disk 324 thatlies between contour 370 and the outside perimeter of themagnetic-recording disk 324 as shown in FIG. 3B, when the hard-diskdrive is inserted into the second portion 524 of the gap. The firstpole-tip portion 516, the second pole-tip portion 536, and the thirdpole-tip portion 572 are configured such that the magnetic-flux densityin the second portion 524 of the gap lies in a substantially radialdirection, for example, similar to radial direction 350 as shown in FIG.3B, of the portion of the magnetic-recording disk of the hard-diskdrive. The first pole-tip portion 516, the second pole-tip portion 536,and the third pole-tip portion 572 are configured to suppressmagnetic-flux density in a third portion of the gap, for example,similar to the third portion 340 described above for FIGS. 3A and 3B,such that the magnetization of the drive-motor magnet of the drive motorin the hard-disk drive is not degraded when located within the thirdportion.

With further reference to FIG. 5, in accordance with an embodiment ofthe present invention, the bulk eraser 501 further includes a yoke 580having a first yoke portion 580 a and a second yoke portion 580 b. Thefirst yoke portion 580 a is magnetically coupled with the first magnet510, the third magnet 560 and the pole piece 570. The second yokeportion 580 b is magnetically coupled with the second magnet 530, thethird magnet 560 and the pole piece 570. The yoke 580 is configured tosuppress stray magnetic flux and to increase magnetic-flux density inthe second portion 524 of the gap. The first yoke portion 580 a mayfurther include a fourth magnet 582 disposed in and magnetically coupledwith the first yoke portion 580 a with polarity assisting magnetic-fluxcirculation in a first magnetic circuit including the first magnet 510,the third magnet 560, the pole piece 570, the second portion 524 of thegap and the first yoke portion 580 a including the fourth magnet 582.The direction 584 of the B-field, the magnetic-flux density, as well asthe magnetization field, in the fourth magnet 582 is shown by the upperarrow in the left leg of the first yoke portion 580 a. The fourth magnet582 may be composed of a high-field-strength, permanent-magnet material,such as NdFeB. The fourth magnet 582 is configured to suppress straymagnetic flux and to increase magnetic-flux density in the secondportion 524 of the gap. The first yoke portion 580 a may further includea sixth magnet 590 disposed in and magnetically coupled with the firstyoke portion 580 a with polarity assisting magnetic-flux circulation inthe first magnetic circuit further including the first yoke portion 580a further including the sixth magnet 590. The direction 592 of theB-field, the magnetic-flux density, as well as the magnetization field,in the sixth magnet 590 is shown by the upper arrow in the top leg ofthe first yoke portion 580 a. The sixth magnet 590 may be composed of ahigh-field-strength, permanent-magnet material, such as NdFeB. The sixthmagnet 590 is configured to suppress stray magnetic flux and to increasemagnetic-flux density in the second portion 524 of the gap.

With further reference to FIG. 5, in accordance with an embodiment ofthe present invention, the second yoke portion 580 b of the bulk eraser501 may further include a fifth magnet 586 disposed in and magneticallycoupled with the second yoke portion 580 b with a polarity assistingmagnetic-flux circulation in a second magnetic circuit including thesecond magnet 530, the third magnet 560, the pole piece 570, the secondportion 524 of the gap and the second yoke portion 580 b including thefifth magnet 586. The direction 588 of the B-field, the magnetic-fluxdensity, as well as the magnetization field, in the fifth magnet 586 isshown by the lower arrow in the left leg of the second yoke portion 580b. The fifth magnet 586 may be composed of a high-field-strength,permanent-magnet material, such as NdFeB. The fifth magnet 586 isconfigured to suppress stray magnetic flux and to increase magnetic-fluxdensity in the second portion 524 of the gap. The second yoke portion580 b may further include a seventh magnet 594 disposed in andmagnetically coupled with the second yoke portion 580 b with polarityassisting magnetic-flux circulation in the second magnetic circuitfurther including the second yoke portion 580 b further including theseventh magnet 594. The direction 596 of the B-field, the magnetic-fluxdensity, as well as the magnetization field, in the seventh magnet 594is shown by the lower arrow in the bottom leg of the second yoke portion580 b. The seventh magnet 594 may be composed of a high-field-strength,permanent-magnet material, such as NdFeB. They seventh magnet 594 isconfigured to suppress stray magnetic flux and to increase magnetic-fluxdensity in the second portion 524 of the gap. At least one magnet of themagnets 510, 530, 560, 582, 586, 590 and 592 may be ahigh-field-strength, permanent magnet, which may be composed of amaterial such as neodymium iron boron, NdFeB. The grade of the NdFeBmaterial used for at least one magnet of the magnets 510, 530, 560, 582,586, 590 and 592 may have a grade between about grade 48 and about grade54; however, a grade of about grade 50 provides a very stable magnet.

With further reference to FIGS. 4A-4C and 5, in accordance withembodiments of the present invention, the bulk eraser includes a firstmagnet having a first end pole and a first pole-tip portion and a secondmagnet having a second end pole and a second pole-tip portion such thatthe first and second magnets are disposed on opposite sides of a firstportion of a gap, and such that the first end pole and the second endpole have same polarity. The bulk eraser also includes a third magnethaving a third end pole of opposite polarity to the first end pole andthe second end pole, and having a pole piece with a third pole-tipportion such that the first pole-tip portion, the second pole-tipportion, and the third pole-tip portion define a second portion of thegap located between the first pole-tip portion, the second pole-tipportion, and the third pole-tip portion. Also, the bulk eraser includesa structure. The structure includes a yoke having a first yoke portionand a second yoke portion. The first yoke portion is magneticallycoupled with the first magnet, the third magnet and the pole piece. Thefirst yoke portion further includes a first plurality of magnetsdisposed in and magnetically coupled with the first yoke portion with apolarity assisting magnetic-flux circulation in a first magnetic circuitincluding the first magnet, the third magnet, the pole piece, the secondportion of the gap and the first yoke portion including the firstplurality of magnets. The structure also includes the second yokeportion magnetically coupled with the second magnet the third magnet andthe pole piece. The second yoke portion further includes a secondplurality of magnets disposed in and magnetically coupled with thesecond yoke portion with a polarity assisting magnetic-flux circulationin a second magnetic circuit including the second magnet, the thirdmagnet, the pole piece, the second portion of the gap and the secondyoke portion including the second plurality of magnets. In accordancewith embodiments of the present invention, the structure is configuredto suppress stray magnetic flux and to increase magnetic-flux density inthe second portion of the gap for erasing recorded information from aportion on the magnetic-recording disk when the hard-disk drive isinserted into the second portion of the gap.

With reference now to FIG. 6, in accordance with an embodiment of thepresent invention, a perspective view 600 of the pole piece 470 of thebulk eraser 401 of FIGS. 4A-4C, similar to the pole piece 570 of thebulk eraser 501 of FIG. 5, disposed on a third end pole 462 of a thirdmagnet 460 disposed in proximity to the second portion 424 of the gapfor concentrating the magnetic-flux density to erase recordedinformation from the portion of the magnetic-recording disk in the HDD,for example, magnetic-recording disk 120 in HDD 100, inserted into thesecond portion 424 of the gap. The first pole-tip portion 416, thesecond pole-tip portion 436, and the third pole-tip portion 472 of thebulk eraser 401 are configured to confine the magnetic-flux density inthe second portion 424 of the gap to a region of the magnetic-recordingdisk sufficiently localized such that strength of eddy currents in themagnetic-recording disk are suppressed when rotating themagnetic-recording disk to erase recorded information on themagnetic-recording disk. The shape of the third pole-tip portion 472 isinstrumental in confining the magnetic-flux density in the secondportion 424 of the gap to a region of the magnetic-recording disksufficiently localized such that strength of eddy currents in themagnetic-recording disk are suppressed when rotating themagnetic-recording disk to erase recorded information on themagnetic-recording disk. A narrow third pole-tip portion 472 confinesthe magnetic-flux density in the second portion 424 of the gap to such asufficiently localized region of the magnetic-recording disk. The shapeof the third pole-tip portion 472 is determined by the shape of the polepiece 470 disposed on the third magnet 460, which is next described. Thepole piece 470 has a wide base 670 to provide as much magnetic flux aspossible to the yoke 480 and a narrow third pole-tip portion 472 toconcentrate the magnetic-flux density in a narrow band about the radialdirection, for example, similar to radial direction 350 of FIG. 3B, ofthe magnetic-recording disk when inserted into the second portion 424 ofthe gap. A pyramid-like shape can provide these functions as nextdescribed.

With further reference to FIG. 6, in accordance with an embodiment ofthe present invention, the pole piece 470 may include a body selectedfrom the group of bodies consisting of a pyramid, a substantiallypyramidally shaped body, a frustum of a rectangular pyramid and afrustum of a substantially pyramidally shaped body having essentially ashape of the frustum of the rectangular pyramid wherein at least one ofplanar lateral faces of the frustum of the rectangular pyramid issubstituted by a concave surface to provide a lateral facing surface 672of the substantially pyramidally shaped body. A first base 670 of thebody is disposed on the third end pole 462 of the third magnet 460, andan apical portion, for example, the third pole-tip portion 472, of thebody is disposed proximate the second portion 424 of the gap. As shownin FIG. 6, a plinth portion of the body may be interposed between thefirst base 670 of the body and the third end pole 462 of the thirdmagnet 460; the plinth portion 674 provides greater mechanical stabilityin mounting the pole piece 470 on the third end pole 462. The apicalportion of a body selected from the group of bodies consisting of thefrustum of the rectangular pyramid and the frustum of the substantiallypyramidally shaped body may be configured as an apical planar surface ofthe body. For example, in the case of the frustum of a pyramid, theapical planar surface is provided by a second base of the frustum of thepyramid adjacent to an apex of a pyramid from which the frustum of thepyramid is derived. The apical portion of the body is elongated in adirection perpendicular to the plane of the magnetic-recording disk tospread magnetic-flux density uniformly over a plurality of planes of aplurality of magnetic-recording disks in the disk-stack of the hard-diskdrive in the second portion 424 of the gap. Thus, at least three magnets410, 430 and 460 and the structure including the third pole-tip portion472 of the pole piece 470 are configured to produce magnetic-fluxdensity such that the magnetic-flux density is applied to a localizedportion of the magnetic-recording disk, aided by the narrow width of thethird pole-tip portion 472, to suppress eddy currents in themagnetic-recording disk of the HDD 100, as previously described above.

With reference now to FIG. 7, in accordance with an embodiment of thepresent invention, a perspective view 700 of the second magnet 430 ofthe bulk eraser 401 of FIGS. 4A-4C, similar to the second magnet 530 ofthe bulk eraser 501 of FIG. 5, is shown. FIG. 7 shows a detailed view ofthe second magnet 430 of the bulk eraser 401, which is disposed inproximity to a first portion 422 of the gap, and the second pole-tipportion 436 of the second magnet 430, which is disposed proximate thesecond portion 424 of the gap for concentrating the magnetic-fluxdensity to erase recorded information from the portion of themagnetic-recording disk in the HDD, for example, magnetic-recording disk120 of HDD 100, when inserted into the second portion 424 of the gap. Asshown in FIG. 7, the second magnet 430 has a second end pole 432 andthat in conjunction with the second pole-tip portion 436 forms a pocketin which second magnetic shield 450 is disposed. The first magnet 410has a first end pole 412 that forms a similar pocket in which the firstmagnetic shield 440 is disposed. The first magnetic shield 440 and thesecond magnetic shield 450 may be composed of a highmagnetic-permeability material. Moreover, the first magnetic shield 440and the second magnetic shield 450 may be composed of a materialselected from the group consisting of low-carbon steel, such as HypercoSteel, permalloy and supermalloy. The magnetic shields 440 and 450provide greater protection for the drive-motor magnet disposed in thefirst portion 422 of the gap by directing magnetic flux away from thedrive-motor magnet. Thus, the magnetic-flux density produced by the atleast three magnets 410, 430 and 460 and the structure, including thefirst magnetic shield 440 in the second magnetic shield 450, isconfigured to erase recorded information from the magnetic-recordingdisk, for example, similar to magnetic-recording disk 324, disposed inthe second portion 424 of the gap without degrading the magnetization ofa drive-motor magnet, for example, similar to drive-motor magnets 330and 334, in the drive motor disposed in the third portion of the gap,for example, similar to the third portion 340 described above for FIGS.3A and 3B. The intensity of a field component of the magnetic-fluxdensity directed along the radial direction, for example, similar toradial direction 350, in the plane of the magnetic-recording disk, forexample, similar to magnetic-recording disk 324, produced by the atleast three magnets 410, 430 and 460 and the structure has a gradient asa function of distance along the radial direction at a transitionregion, similar to the transition region described above for FIG. 3B,between the second portion 424 of the gap and the third portion, forexample, similar to the third portion 340 described above for FIGS. 3Aand 3B, of the gap such that the gradient allows erasing recordedinformation from the magnetic-recording disk in close proximity to thedrive-motor magnet, for example, similar to drive-motor magnets 330 and334, in the drive motor without degrading the magnetization of thedrive-motor magnet in the drive motor. Modeling results for the gradientin the magnetic-flux density at the transition region in an alternativeembodiment of the present invention, which utilizes five magnets, arenext described.

With reference now to FIG. 8, in accordance with an embodiment of thepresent invention, a plot 800 of the intensities of the magnetic fieldintensity as a function of radial distance from center of a disk in theplane of each of four magnetic-recording disks in a disk-stack of a HDDinserted into the second portion of the gap of a bulk eraser is shown.The bulk eraser is configured with five magnets, similar to magnets 510,530, 560, 582 and 586 of the bulk eraser 501 of FIG. 5, to eraserecorded information from magnetic-recording disks in a disk-stack of anHDD in the second portion of the gap, similar to the second portion 524of the gap of the bulk eraser 501. Ordinate 804 of the plot 800 of theintensities of the magnetic field intensity (magnetic-flux density) isgiven in units of Oersteds (Oe) to erase a magnetic-recording disk.Abscissa 808 of the plot 800 is given in units of millimeters (mm) ofdisk radius. The direction of the abscissa 808 is from right to leftrather than left to right to facilitate comparison with the earlierplots of the distribution of magnetic field intensity (magnetic-fluxdensity) of FIGS. 3A and 3B. The location of the OD of the disk alongthe radius of the magnetic-recording disk is indicated by the verticalline 870. The location of the ID of the disk along the radius of themagnetic-recording disk is indicated by the vertical line 872. Thelocation of the OD of the drive motor along the radius of themagnetic-recording disk is indicated by the vertical line 880. The erasefield necessary to erase recorded information from themagnetic-recording disk is indicated by the horizontal line 850, whichis approximately 7500 Oe. The critical field to degrade themagnetization of a drive-motor magnet is indicated by the horizontalline 860, which is approximately 3000 Oe.

With further reference to FIG. 8, in accordance with an embodiment ofthe present invention, four plots 810, 820, 830 and 840, one for each offour disks in a disk-stack, are given for the magnitude of themagnetic-flux-density vector along a radial direction of themagnetic-recording disk in the HDD that is oriented substantiallyparallel to the central flux-propagation direction in the bulk eraser.Plot 810 is for disk 1 in the disk-stack; plot 820 is for disk 2 in thedisk-stack; plot 830 is for disk 3 in the disk-stack; and, plot 840 isfor disk 4 in the disk-stack. Each of the plots 810, 820, 830 and 840shows the behavior of the magnitude of the magnetic-flux-density vectoralong the radial direction as a function of distance from the center ofeach of the disks: disk 1, disk 2, disk 3 and disk 4, respectively. Asshown in FIG. 8, each of the plots 810, 820, 830 and 840 crosses thehorizontal line 850 corresponding to the erase field necessary to eraserecorded information from the magnetic-recording disk at about a radiusof 21 mm. Therefore, any portion of the magnetic-recording disk greaterthan a radius of 21 mm will be erased. Thus, the radius of 21 mmcorresponds roughly to the location of a contour in the magnitude of themagnetic-flux-density vector similar to contour 370 shown in FIG. 3B. Onthe other hand, any portion of the magnetic-recording disk less than aradius of 21 mm will not be erased. Therefore, the region between whereeach of the plots 810, 820, 830 and 840 crosses the horizontal line 850,at about 21 mm, and the vertical line 880, which designates the locationof the OD of the drive motor, corresponds roughly to the transitionregion in the gap, similar to the transition region in the gap shown inFIG. 3B.

With further reference to FIG. 8, in accordance with an embodiment ofthe present invention, it is desirable to make the transition region assmall as possible to minimize the amount of time required to eraseportions of a disk that lie between the crossing of the plots 810, 820,830 and 840, at about 21 mm, and the vertical line 872 corresponding tothe ID of a disk. This can be accomplished by making the gradient of themagnetic-flux density as a function of radius as great as possible inthis transition region, which can be effectuated by making themagnetic-flux density in the erasing region greater than 21 mm as highas possible while minimizing the magnetic-flux density at the locationof the drive motor. Moreover, as shown in FIG. 8, the plots 810, 820,830 and 840 cross the horizontal line 860 corresponding to the criticalfield for degrading the magnetization of drive-motor magnets at about 10mm. Thus, to erase the maximum portion of the disks, it is desirable toemploy a stroke length that brings the OD of the motor right up to thecrossing point where the plots cross the horizontal line 860corresponding to the critical field for degrading the magnetization ofthe drive-motor magnets. In accordance with embodiments of the presentinvention, the intensity of a field component of the magnetic-fluxdensity directed along the radial direction in the plane of themagnetic-recording disk produced by five magnets, similar to magnets510, 530, 560, 582 and 586, and the structure has a gradient as afunction of distance along the radial direction at a transition region,similar to the transition region described above for FIG. 3B, betweenthe second portion of the gap and the third portion of the gap such thatthe gradient allows erasing recorded information from themagnetic-recording disk in close proximity to the drive-motor magnet,for example, similar to drive-motor magnets 330 and 334, in the drivemotor without degrading the magnetization of the drive-motor magnet inthe drive motor. Similarly, as shown by the modeling results of FIG. 8,the first pole-tip portion, the second pole-tip portion, and the thirdpole-tip portion of the bulk eraser utilizing the five magnets, similarto magnets 510, 530, 560, 582 and 586 of bulk eraser 501, are configuredto suppress magnetic-flux density in a third portion of the gap suchthat the magnetization of the drive-motor magnet of the drive motor inthe hard-disk drive is not degraded when located within the thirdportion.

Description of Embodiments of the Present Invention for a Method ofManufacturing of a Hard-Disk Drive using a Bulk Eraser for ErasingRecorded Information on a Magnetic-Recording Disk

With reference now to FIGS. 9A and 9B, in accordance with an embodimentof the present invention, a flow chart 900 illustrates the method ofmanufacturing of a HDD using a bulk eraser for erasing recordedinformation on a magnetic-recording disk. At 910, a bulk eraser thatproduces magnetic-flux density in a second portion of a gap sufficientto erase recorded information from a portion of the magnetic-recordingdisk, a HDD having an enclosure, a disk-stack having at least onemagnetic-recording disk rotatably mounted on a spindle, and a drivemotor having a rotor attached to the spindle for rotating themagnetic-recording disk inside the enclosure are provided. At 920, aplurality of magnets and a structure of the bulk eraser are configuredsuch that magnetic-flux density is oriented substantially parallel to acentral plane in the second portion of the gap and in a substantiallyradial direction of the portion of the magnetic-recording disk when theHDD is inserted into the second portion of the gap. At 930, themagnetic-recording disk is rotated in the HDD. At 940, the HDD isinserted into the second portion of the gap of the bulk eraser such thata plane of the magnetic-recording disk of the HDD is orientedsubstantially parallel to the central plane in the second portion of thegap such that magnetic-flux density is oriented in the substantiallyradial direction of the portion of the magnetic-recording disk. At 950,recorded information is erased from the portion of themagnetic-recording disk in the HDD located in the second portion of thegap. At 960, the HDD is removed from the second portion of the gap.

With reference now to FIG. 10, in accordance with an embodiment of thepresent invention, a flow chart 1000 illustrates further embodiments ofthe present invention for a method of manufacturing of a HDD using abulk eraser for erasing recorded information on a magnetic-recordingdisk. At 1010, pole pieces of the structure and pole-tip portions of thepole pieces are configured such that magnetic-flux density in the secondportion of the gap is oriented substantially parallel to a centralflux-propagation direction in the second portion of the gap. At 1020,the magnetic-recording disk in the HDD is oriented such that a radialdirection of the portion of the magnetic-recording disk is orientedsubstantially parallel to the central flux-propagation direction in thesecond portion of the gap.

With reference now to FIG. 11, in accordance with an embodiment of thepresent invention, a flow chart 1100 illustrates further embodiments ofthe present invention for a method of manufacturing of a HDD using abulk eraser for erasing recorded information on a magnetic-recordingdisk. At 1110, the HDD is inserted into the second portion of the gapwith an insertion speed that is sufficient to assure complete erasure ofrecorded information on the magnetic-recording disk in the HDD. At 1120,the insertion of the hard disk drive into the second portion of the gapis such that an insertion speed into the gap is less than or equal to 1centimeter per second.

With reference now to FIG. 12, in accordance with an embodiment of thepresent invention, a flow chart 1200 illustrates further embodiments ofthe present invention for a method of manufacturing of a HDD using abulk eraser for erasing recorded information on a magnetic-recordingdisk. At 1210, the HDD is removed from the second portion of the gapwith a speed that is sufficient to assure complete erasure of recordedinformation on the magnetic-recording disk in the HDD. At 1220, theremoval of the hard disk drive from the second portion of the gap issuch that the removal speed from the gap is less than or equal to 1centimeter per second.

With reference now to FIG. 13, in accordance with an embodiment of thepresent invention, a flow chart 1300 illustrates further embodiments ofthe present invention for a method of manufacturing of a HDD using abulk eraser for erasing recorded information on a magnetic-recordingdisk. At 1310, the magnetic-recording disk in the HDD is rotated withthe drive motor at a rotation speed that is sufficient to assurecomplete erasure of recorded information on the magnetic-recording diskin the HDD without stalling the drive motor. At 1320, the rotation ofthe magnetic-recording disk in the hard disk drive is such that therotation speed of the magnetic-recording disk is less than or equal to 2Hertz.

With reference now to FIG. 14, in accordance with an embodiment of thepresent invention, a flow chart 1400 illustrates further embodiments ofthe present invention for a method of manufacturing of a HDD using abulk eraser for erasing recorded information on a magnetic-recordingdisk. At 1410, a low speed drive-motor-driver circuit is providedon-board in the HDD to provide power to the drive motor to rotate themagnetic-recording disk at a slow speed to prevent stalling of the drivemotor. At 1420, power is provided to the low speed drive-motor-drivercircuit on-board in the HDD. At 1430, the power provided is such that acable and connector, attached to an external power supply, is attachedto the HDD.

With reference now to FIG. 15, in accordance with an embodiment of thepresent invention, a flow chart 1500 illustrates further embodiments ofthe present invention for a method of manufacturing of a HDD using abulk eraser for erasing recorded information on a magnetic-recordingdisk. At 1510, the second portion of the gap is provided with sufficientclearance to accommodate the HDD upon inserting and removing the HDDfrom the second portion of the gap. At 1520, the clearance in the secondportion of the gap is such that the clearance of the second portion ofthe gap is less than or equal to about 2.6 centimeters.

With reference now to FIG. 16, in accordance with an embodiment of thepresent invention, a flow chart 1600 illustrates further embodiments ofthe present invention for a method of manufacturing of a HDD using abulk eraser for erasing recorded information on a magnetic-recordingdisk. At 1610, a fixture is provided for rapidly and reproduciblyaligning the HDD in the second portion of the gap. At 1620, the fixtureis such that the fixture limits a stroke length upon inserting the HDDinto the second portion of the gap such that the magnetic-flux densityproduced by the plurality of magnets and the structure is configured toerase recorded information from the portion of the magnetic-recordingdisk disposed in the second portion of the gap without degrading themagnetization of a drive-motor magnet in the drive motor disposed in athird portion of the gap.

With reference now to FIG. 17, in accordance with an embodiment of thepresent invention, a flow chart 1700 illustrates further embodiments ofthe present invention for a method of manufacturing of a HDD using abulk eraser for erasing recorded information on a magnetic-recordingdisk. At 1710, two magnets of the plurality of magnets are disposed withopposing polarity across a first portion of the gap. At 1720, aseparation between the two magnets of the plurality of magnets in thefirst portion of the gap is adjusted such that the first portion of thegap has sufficient clearance to accommodate the HDD upon inserting andremoving the HDD from the second portion of the gap and themagnetic-flux density produced by the plurality of magnets and thestructure is sufficient to erase recorded information from a pluralityof magnetic-recording disks of the disk-stack when the HDD is insertedinto the second portion of the gap.

With reference now to FIGS. 18A and 18B, in accordance with anembodiment of the present invention, a flow chart 1800 illustrates themethod of reworking a HDD in manufacturing the HDD using a bulk eraserfor erasing a servo pattern on a magnetic-recording disk. At 1810, abulk eraser that produces magnetic-flux density in a second portion of agap sufficient to erase a first servo pattern from a portion of themagnetic-recording disk, a HDD having an enclosure, a disk-stack havingat least one magnetic-recording disk rotatably mounted on a spindle, anda drive motor having a rotor attached to the spindle for rotating themagnetic-recording disk inside the enclosure are provided. At 1820, aplurality of magnets and a structure of the bulk eraser are configuredsuch that magnetic-flux density is oriented substantially parallel to acentral plane in the second portion of the gap and in a substantiallyradial direction of the portion of the magnetic-recording disk when theHDD is inserted into the second portion of the gap. At 1830, themagnetic-recording disk is rotated in the HDD. At 1840, the HDD isinserted into the second portion of the gap of the bulk eraser such thata plane of the magnetic-recording disk of the HDD is orientedsubstantially parallel to the central plane in the second portion of thegap such that magnetic-flux density is oriented in the substantiallyradial direction of the portion of the magnetic-recording disk. At 1850,the first servo pattern is erased from the portion of themagnetic-recording disk in the HDD located in the second portion of thegap. At 1860, the HDD is removed from the second portion of the gap. At1870, a second servo pattern is written on the magnetic-recording diskin the HDD to replace the first servo pattern.

With reference now to FIGS. 19A and 19B, in accordance with anembodiment of the present invention, a flow chart 1900 illustrates themethod of preserving security of recorded information in a HDD in acomputer system using a bulk eraser. At 1910, the HDD is removed fromthe computer system. At 1920, a bulk eraser that produces magnetic-fluxdensity in a second portion of a gap sufficient to erase recordedinformation from a portion of the magnetic-recording disk, a HDD havingall enclosure, a disk-stack having at least one magnetic-recording diskrotatably mounted on a spindle, and a drive motor having a rotorattached to the spindle for rotating the magnetic-recording disk insidethe enclosure are provided. At 1930, a plurality of magnets and astructure of the bulk eraser are configured such that magnetic-fluxdensity is oriented substantially parallel to a central plane in thesecond portion of the gap and in a substantially radial direction of theportion of the magnetic-recording disk when the HDD is inserted into thesecond portion of the gap. At 1940, the magnetic-recording disk isrotated in the HDD. At 1950, the HDD is inserted into the second portionof the gap of the bulk eraser such that a plane of themagnetic-recording disk of the HDD is oriented substantially parallel tothe central plane in the second portion of the gap such thatmagnetic-flux density is oriented in the substantially radial directionof the portion of the magnetic-recording disk. At 1960, recordedinformation is erased from the portion of the magnetic-recording disk inthe HDD located in the second portion of the gap. At 1970, the HDD isremoved from the second portion of the gap.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and many modifications andvariations are possible in light of the above teaching. The embodimentsdescribed herein were chosen and described in order to best explain theprinciples of the invention and its practical application, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as are suited to theparticular use contemplated. It may be intended that the scope of theinvention be defined by the claims appended hereto and theirequivalents.

1. A bulk eraser for erasing recorded information on amagnetic-recording disk in a hard-disk drive, said bulk erasercomprising: a first magnet disposed opposite a second magnet across afirst portion of a gap, said first magnet having a first end poledisposed proximate said first portion of said gap and a first pole-tipportion disposed proximate a second portion of said gap, and said secondmagnet having a second end pole disposed proximate said first portion ofsaid gap and a second pole-tip portion disposed proximate said secondportion of said gap, wherein said first and second end poles have a samepolarity; a first magnetic shield disposed on said first end pole inproximity to said first portion of said gap; a second magnetic shielddisposed on said second end pole in proximity to said first portion ofsaid gap; a third magnet disposed proximate to a second portion of saidgap, said third magnet having a third end pole disposed proximate saidsecond portion of said gap, wherein said third end pole has a polarityopposite to said first and second end poles; and a pole piece disposedon said third end pole in proximity to said second portion of said gap,said pole piece having a third pole-tip portion wherein said pole pieceis shaped to concentrate magnetic-flux density in said second portion ofsaid gap substantially parallel to said plane of said magnetic-recordingdisk in said disk-stack of said hard-disk drive in said second portionof said gap wherein said pole piece further comprises: a body selectedfrom the group of bodies consisting of a pyramid, a substantiallypyramidally shaped body, a frustum of a rectangular pyramid and afrustum of a substantially pyramidally shaped body having essentially ashape of said frustum of said rectangular pyramid wherein at least oneof planar lateral faces of said frustum of said rectangular pyramid issubstituted by a concave surface to provide a lateral facing surface ofsaid substantially pyramidally shaped body; wherein a first base of saidbody is disposed on said third end pole of said third magnet, and anapical portion of said body is disposed proximate said second portion ofsaid gap; wherein said apical portion of said body selected from thegroup of bodies consisting of said frustum of said rectangular pyramidand said frustum of said substantially pyramidally shaped body isconfigured as an apical planar surface of said body; and wherein saidapical portion of said body is elongated in a direction perpendicular tosaid plane of said magnetic-recording disk to spread magnetic-fluxdensity uniformly over a plurality of planes of a plurality ofmagnetic-recording disks in said disk-stack of said hard-disk drive insaid second portion of said gap; wherein said first pole-tip portion,said second pole-tip portion, and said third pole-tip portion define asecond portion of said gap located between said first pole-tip portion,said second pole-tip portion, and said third pole-tip portion and areconfigured such that magnetic-flux density in said second portion ofsaid gap lies substantially parallel to a plane of saidmagnetic-recording disk in a disk-stack of said hard-disk drive to eraserecorded information from a portion on said magnetic-recording disk whensaid hard-disk drive is inserted into said second portion of said gap.2. The bulk eraser of claim 1, wherein said first magnetic shield andsaid second magnetic shield are composed of a high magnetic-permeabilitymaterial.
 3. The bulk eraser of claim 2, wherein said first magneticshield and said second magnetic shield are composed of a materialselected from the group consisting of low-carbon steel, permalloy andsupermalloy.
 4. The bulk eraser of claim 1, wherein said first pole-tipportion, said second pole-tip portion, and said third pole-tip portionare configured such that said magnetic-flux density in said secondportion of said gap lies in a substantially radial direction of saidportion of said magnetic-recording disk of said hard-disk drive.
 5. Thebulk eraser of claim 1, wherein said first pole-tip portion, said secondpole-tip portion, and said third pole-tip portion are configured tosuppress magnetic-flux density in a third portion of said gap such thatmagnetization of said drive-motor magnet of said drive motor in saidhard-disk drive is not degraded when located within said third portion.6. The bulk eraser of claim 1, wherein said first pole-tip portion, saidsecond pole-tip portion, and said third pole-tip portion are configuredto confine said magnetic-flux density in said second portion of said gapto a region of said magnetic-recording disk sufficiently localized suchthat strength of eddy currents in said magnetic-recording disk aresuppressed when rotating said magnetic-recording disk to erase recordedinformation on said magnetic-recording disk.
 7. The bulk eraser of claim1, wherein said first pole-tip portion is configured to direct magneticflux emanating from said first pole-tip portion to said third pole-tipportion and is configured to concentrate magnetic-flux density in saidsecond portion of said gap substantially parallel to said plane of saidmagnetic-recording disk in said hard-disk drive in said second portionof said gap; wherein said second pole-tip portion is configured todirect magnetic flux emanating from said second pole-tip portion to saidthird pole-tip portion and is configured to concentrate magnetic-fluxdensity in said second portion of said gap substantially parallel tosaid plane of said magnetic-recording disk in said hard-disk drive insaid second portion of said gap; and wherein said third pole-tip portionis configured to receive said magnetic flux emanating from said firstpole-tip portion and said magnetic flux emanating from said secondpole-tip portion and to concentrate magnetic-flux density in said secondportion of said gap substantially parallel to said plane of saidmagnetic-recording disk in said hard-disk drive in said second portionof said gap.
 8. The bulk eraser of claim 1, wherein said third pole-tipportion is configured to direct a first portion of magnetic fluxemanating from said third pole-tip portion to said first pole-tipportion and to direct a second portion of magnetic flux emanating fromsaid third pole-tip portion to said second pole-tip portion and toconcentrate magnetic-flux density in said second portion of said gapsubstantially parallel to said plane of said magnetic-recording disk insaid hard-disk drive in said second portion of said gap; wherein saidfirst pole-tip portion is configured to receive said first portion ofmagnetic flux emanating from said third pole-tip portion and isconfigured to concentrate magnetic-flux density in said second portionof said gap substantially parallel to said plane of saidmagnetic-recording disk in said hard-disk drive in said second portionof said gap; and wherein said second pole-tip portion is configured toreceive said second portion of magnetic flux emanating from said thirdpole-tip portion and is configured to concentrate magnetic-flux densityin said second portion of said gap substantially parallel to said planeof said magnetic-recording disk in said hard-disk drive in said secondportion of said gap.
 9. The bulk eraser of claim 1, wherein at least oneof said first magnet, said second magnet and said third magnet is ahigh-field-strength, permanent magnet.
 10. A bulk eraser for erasingrecorded information on a magnetic-recording disk in a hard-disk drive,said bulk eraser comprising: a first magnet disposed opposite a secondmagnet across a first portion of a gap, said first magnet having a firstend pole disposed proximate said first portion of said gap and a firstpole-tip portion disposed proximate a second portion of said gap, andsaid second magnet having a second end pole disposed proximate saidfirst portion of said gap and a second pole-tip portion disposedproximate said second portion of said gap, wherein said first and secondend poles have a same polarity; a first magnetic shield disposed on saidfirst end pole in proximity to said first portion of said gap; a secondmagnetic shield disposed on said second end pole in proximity to saidfirst portion of said gap; a third magnet disposed proximate to a secondportion of said gap, said third magnet having a third end pole disposedproximate said second portion of said gap, wherein said third end polehas a polarity opposite to said first and second end poles; and a polepiece disposed on said third end pole in proximity to said secondportion of said gap, said pole piece having a third pole-tip portion;wherein said first pole-tip portion, said second pole-tip portion, andsaid third pole-tip portion define a second portion of said gap locatedbetween said first pole-tip portion, said second pole-tip portion, andsaid third pole-tip portion and are configured such that magnetic-fluxdensity in said second portion of said gap lies substantially parallelto a plane of said magnetic-recording disk in a disk-stack of saidhard-disk drive to erase recorded information from a portion on saidmagnetic-recording disk when said hard-disk drive is inserted into saidsecond portion of said gap; a yoke having a first yoke portion and asecond yoke portion; said first yoke portion magnetically coupled withsaid first magnet, said third magnet and said pole piece; and saidsecond yoke portion magnetically coupled with said second magnet, saidthird magnet and said pole piece; wherein said yoke is configured tosuppress stray magnetic flux and to increase magnetic-flux density insaid second portion of said gap wherein said first yoke portion furthercomprises: a fourth magnet disposed in and magnetically coupled withsaid first yoke portion with polarity assisting magnetic-fluxcirculation in a first magnetic circuit comprising said first magnet,said third magnet, said pole piece, said second portion of said gap andsaid first yoke portion including said fourth magnet; wherein saidfourth magnet is composed of a high-field-strength, permanent-magnetmaterial; and wherein said fourth magnet is configured to suppress straymagnetic flux and to increase magnetic-flux density in said secondportion of said gap.